The button for merging accounts disappeared on my discourse website. We did just change some versioning. We were on the beta branch, but we change to the ‘normal’. So currently we are running version 3.4.1
Is merging account available in this version?
Hi Theodores! Welcome to our community! 
Can you confirm that the user you are trying to merge into another user is not an admin or moderator? You can’t merge admins and moderators. I just checked and I do see the Merge button at the bottom of the user admin page, for regular site members.
Thanks for the quick reply!
The user is not an admin and is also not a moderator.
Although you reply made me realise that I was logged in as a moderator, but not admin. The admin account can merge users!
Ah ha! That makes sense too. 