Look under your toilet tank to the left side and see if you have a isolation valve OR possibly a tile stop valve. Once you shut the CW supply you can then disconnect the tank supply (If it is a tank and bowl in lieu of a flushometer) and then losen the flange floor bolts.
Nex get a deep seal wax gasket (Horn type) and install new brass bolts GENTLY making up each side evenly. If you over tighten you WILL BREAK the toilet if under tightned your toilet will rock and end up destroying your floor flange connection.
If you hire a licensed Master plumber you wont have to worry as much huh?
SylvanLMP