OpenStreetMap is a live database. Edits are reflected immediately. I presume you are referring to the standard Carto layer used as a basemap on openstreetmap.org. This means an old version of the tile is cached on your device. Assuming you're viewing on OpenStreetMap.org, you can force refresh (probably Ctrl-Shift-R) to load the newest version of the tile.

If you are using a different tileset, it may take longer for the update to be visible.

To confirm that the changes are in place, use the Layers menu and check the "Map Data" overlay. You will be able to click the building and view tags and other way information.