uac - Give admin privilege with a fully limited user windows 7 professional

i by accident made myself into Administrator for networking purposes; this i thought at first wouldn't be a problem but then i noticed.

I am a paranoid person, i have my UAC maxed, so without admin verification i cannot install nor more or overwrite files. Now, since i do not know the administrators password i cannot do this; it doesn't even work to go into cmd. "Allowance denied"

I am this limited so that all i really can do i use the computer without making a change. This is an old computer of mine and administrator password for the other user is impossible for me to remember since it's my ex-wifes account.

Please help me out, i tried system rollback but that needs UAC verification.