If you have Windows 8.1 you need to run the notepad application as administrator:
1. press start;
2. type notepad in windows search bar
3. right click on the notepad application icon
4. click on run as administrator
Once the notepad is opened:
1. press on "file" -> "open.."
2. go to the wow installation folder and then in the WTF folder
3. you can't see the config.wtf file until you change the notepad extension from " text file*.txt " to " all files *.* " in the bottom-right of the window
4. click on config.wtf file to open it
5. change the realmlist and save it
Did it!

