Get the engine to TDC using your dial gauge (or long screwdriver/suitable stick) and see if the cam locks bolt on. If they do, the timing is correct (as it should be) and you can go ahead, change the belt, set the tension, and check all's well by removing the cam locks, rotating the engine a few times, getting it back to TDC and refitting the cam locks. If that's all good, then job done.
Of course if the cam locks don't fit at the start, then you'll need to loosen the cam pulleys. If you're confident in improvising with whatever tools you have to hand then no big deal. Otherwise, you'll need the correct tools. From memory, one of the cam pulleys (inlet cam I think) is held on with 4 cap screws or similar, so no need to hold the pulley to undo those. Just the exh cam one.
It's all pretty straightforward really, you're just replacing a toothed rubber drive belt and associated bits, not performing brain surgery.