Well, I finally found this out after combining results of multiple searches on the internet.
First, go to C:\WINDOWS\system32 and then search for sethc.exe. Rename it to sethc.exe.old and then find cmd. Copy that and make another one. Then rename the copy to sethc.exe and restart the computer. Then, before you log on, press SHIFT repeatly until you hear a beep. Then type the following in the CMD line that's going to run:
net localusers administrators USERNAME /add
Replace USERNAME with the limited account's username.
Now you log onto your account and it should be a administrative account!
To replace sethc.exe so nobody gets any ideas, go to C:\WINDOWS\system32, find sethc.exe and delete it. Then rename sethc.exe.old to sethc.exe and that will do it!
Remember to delete system restore points (optional)
And This page's history (optional)
And to delete this from the recycle bin (optional)
I hope this helped someone.