You can not change your username if you are not donators, VIP members or you don't have big contributions in the community.
The exception is if your username has personal information that can put you under dox attack. I think your username is not this case.
Done. Now only moderators, Donators, and VIP members can change their names automatically. Other members should contact me. I'll probably ignore your request if you have less than 50 posts (unless your posts are very good).
You can't. You can try PM an admin and they may do it, but they usually don't. You can just create another account with that name if you feel like you need it.