gatepc wrote: Even though my friend has admin privileges
How did you give it to them?
If they have ANY Admin permissions, they should see a link to the ACP in the footer of the board.
and even has a rank that says "site admin"
Ranks are purely cosmetic. They give no powers at all.
As the above poster stated, adding them to the "Administrators" group should give them most powers.
Be very careful who you give "founder" status to. A new founder can easily demote the original founder.