on one of them, cut any page content, then change the category page to
{{Rename Category|name of the other category page}}
save it, if you did it correct, the other page will be shown in the link as existing (in black) and not needed (in red)
go to the other page and paste in the content from the 1st page, merge the info together deleting duplicate data
save it.
within about 12 hours, if EditBot is not doing a lot of updates from the previous cycle, it will go into all of the profiles that used the 1st category and change them to use the 2nd category
if all goes well, the 1st category will be deleted, if there are profiles or something else that had something more than just the link or too many profiles to update, the rename will be put into a manual cleanup or need confirmation to rename. anyone can do the manual updates, only a few people have the authority to confirm large numbers of renames.