FMG Name Changing

Hello, I like to change my name, FireMonkeyGamer, into FMG. The thing is that I have the account FMG on smogon. I know you aren't suppose to my make another account on smogon if you already have one, hence the reason why you have the name changing thread, BUT I didn't make this account (FMG). My cousin actually made this account when he was at my house. I don't know why he made this account because he doesn't even play pokemon anymore nor does he care about smogon. I would have stopped him if I knew he was making an account called FMG b/c I was planning to change my name into FMG. He asked me what he should name his account and I wasn't paying attention so I accidentally said "FMG" because I was doing my hw. He made the account but he never used it ever since that day. After few days, I thought I would request my name change into FMG but then I found out FMG on smogon was already taken. Then I realized it was my cousin who made the account few days ago. I asked him if he uses it or not, and he said no. He said he just made the account for the fucks of it, he doesn't care about it. I asked him if I could have the account and he said sure. So basically, I want to change my name into FMG but I don't know how the process would work now because FMG is already taken on smogon but I know the password and everything. So is there a way to change my name into FMG and not lose my voice in ou room, my messages/history on smogon, etc. I know this is my fault for letting my cousin make the account, I wish i wasn't that dumb for letting him do that. I wanted to talk to you about it and see what you think about this. So is there a way to transport FireMonkeyGamer into FMG or something like that. I just want the name FMG. Sorry for this long story. Hopefully you understand.

PROOF THAT I HAVE FMG ACCOUNT: http://prntscr.com/ci4xl8  http://prntscr.com/ci4y3g