Having issues changing my Realmlist

[Bonneh]

I have downloaded vanilla > Tbc > 2.4.3(and all patches supplied with the Download link) but when trying to change the realmlist I get an error saying
"Realmlist.exe already exists"
and then when I try to replace it I get
"Access not granted"
Anyone able to help me out with this one
also when I try and go on the client at moment it will try and download me to 4.0, I'm guessing this is to do with the realmlist aswell? any help is appreciated, Thanks

[Henhouse]

This is due to permissions on Windows. Either disable UAC or right-click "Run As Administrator."

[Bonneh]

That sorted it, cheers man