Username changes for regular members are done once every year around Christmas whereas VIP's have a name change on every third month (March, June, September, December).
If I was to be honest you should have thought more wisely on the username you wanted to have when registering. If you want a name change you would either have to wait until Christmas or upgrade to VIP. If you introduce the system where you can change your name by yourself users should only be able to have 1 name change per year, and VIP's would be able to have 1 every 3 months. But I am no expert on these things and I'm not sure if it works that way. You should try to contact someone who is more of an expert when it comes to vBulletin or mention it to the staff and they can discuss it from there. It's probably the way it is at the moment to prevent confusion between the members and the staff.
Although VIP's have the privilege to change their name every 3 months, not many actually do. They aren't spoilt.
Originally Posted by Canvas
How would you know what usernames have already been taken? Or whether it'd glitch your profile?
It will probably be like when you register. If you try to register with a name that's already taken it informs you, so I guess it's the same way as that.