Hey GOduori,

Do not reclassify highways without proper reason, please.

This road is unlikely to be a secondary road.
- It only connects two secondary roads (and minor/private roads), not directly i.e. two residential areas.
- It was previously classified as 'unclassified', which in OpenStreetMap (OSM)-terms means
'minor road', see
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dunclassified
Other roads in this area are also minor or tertiary, depending on their restrictions.
- It goes through a park, which might indicate restrictions / ownership.
- It is gated on both sides, which might indicate a possible physical barrier and restrictions / ownership.

It is not even possibly through-road.
Go to 'Edit' (this is the editor called 'iD'), and in the right sidebar click on 'Data Layers', scroll down to 'Photo Overlays'(street-level imagery) and choose Mapillary.
(there is a 'Date range' slider below)
- Destinations signed are minor; park, zoo..
(there is not clear image of all signs)
https://www.mapillary.com/app/?pKey=259616369186816&focus=photo
- It is signed as prohibiting 'commercial vehicles'.
https://www.mapillary.com/app/?pKey=1762891911107468&focus=photo
- The maxspeed is 30 km/h
https://www.mapillary.com/app/?pKey=1323198022270691&focus=photo
- Further down it is one-way single lane road
https://www.mapillary.com/app/?pKey=1186875451742658&focus=photo
- then becomes a 'No through traffic' / 'cul de sac'
https://www.mapillary.com/app/?pKey=142607761165803&focus=photo
- which ends at row of bollards at both ends
https://www.mapillary.com/app/?pKey=795899111312268&focus=photo
(at this way segment 
https://www.openstreetmap.org/way/1037781266/history ); though image is from 2018.
- Onto Acres road there is a stop sign, so way does not have priority.
https://www.mapillary.com/app/?pKey=278653290630379&focus=photo
- Also last segment is one-way road in opposite direction, without priority.
https://www.mapillary.com/app/?pKey=1480276479182064&focus=photo

From your changeset comment, this change was based solely on getting improper/missing result(s) from a query using overpass.
From your changeset details, it is likely you used only the Bing aerial imagery (which, though it is the best in this area, is also the standard imagery in the iD editor); this is understandable, as you are a relatively new contributor.
However, it seems not based on survey, local knowledge (which may include news article), sources available in the editor or other compatible source (not proprietary/copyright, i.e. not Google Maps), nor does it explicitly mention a proper reason for reclassifying these highways in the changeset comment.

Incorrect result by such applications is usually an error in the query, or alternatively application, not directly in the map data.

Changing map data in such way is considered 'Mapping for external application' and is prohibited by OSM guidelines;
Changing map data (usually incorrectly) for application (i.e. renderer, browser, router, validator etc.) to return results solely for personal (sometimes malicious) reasons (i.e. different use / avoiding dev. work, decorative, opiniated/political, etc.). See also
https://wiki.openstreetmap.org/wiki/Tagging_for_the_renderer

Make sure to follow the (local) guidelines or concensus on for example tags for highways.
https://wiki.openstreetmap.org/wiki/United_Kingdom#Guidelines

Be careful when changing highways, especially reclassifications but also roads with relations (i.e. bus routes, turn restrictions). Editing these without prior knowledge, especially with the basic iD editor, might accidentally introduce errors (moving nodes, disordering or breaking relations). It is better to make such advanced changes with more experience and JOSM editor.
https://wiki.openstreetmap.org/wiki/JOSM
(Changes on larger scale should be discussed prior with the (local) community.)

Also, you should provide a proper description and reason of your changes in your changeset comment when saving (preferably for most if not all changesets), so other mappers can understand and validate your changes more easily.
https://wiki.openstreetmap.org/wiki/Good_changeset_comments

For other helpful tips, see
https://wiki.openstreetmap.org/wiki/Good_practice

If you have made any other changes which could be considered similarly incorrect, you should request them to be reverted by contacting the Data Working Group (DWG)
https://osmfoundation.org/wiki/Data_Working_Group#I.27ve_seen_a_problem.3B_what_should_I_do.3F

If you have any questions regarding how to contribute / map, you can contact your (local) community at
https://openstreetmap.community/
or start a thread on the forums
https://community.openstreetmap.org/

This changeset was fully reverted in
https://www.openstreetmap.org/changeset/166693897

Your changes visualised
https://overpass-api.de/achavi/?changeset=166574769

Regards,

Daniel