Users with dots in their name cannot upload a profile photo! Delete User???

A few members on my network have created usernames which have dots in them. It seems that this is preventing them from uploading a profile photo of themselves. I cannot find any way to edit their usernames (version 1.6). I read that one should never, ever delete a user. Any ideas what I should do? I need to get this sorted. Thanks in advance for any help. I'm a newbie by the way.