You're not the first to have the feeling that this can't be so simple :-) But indeed if the relation is complete, you just need four actions in total, whatever the number of members is: select a member of the relation, then click the "download relation" button at the right of the relation's name, then click the "delete" button just at the right of the "download" button, then re-add the member to the relation. You're done!

I'll do this here and you can try another time :-)