It's not hard and the directions are correct, even if the googlemap highlights the underpasses on the Westlink rather than the roundabouts.
Get to the end of the M1, you'll be at the Boucher Road rbt. Join the Westlink heading in the direction of the city centre/M2/northbound (straight on).
I'm advised that roadworks ongoing on the M1/Westlink area aren't as bad as they were, but if you are running to a deadline, it would be best leave a bit of extra time.
The junction to exit is the next one - you should see the signs for the city centre. Take the slip road and the Grosvenor Rd rbt is a fairly large with slightly confusing lanes. You are taking it right in the direction of the city centre (left takes you towards the Falls Road). Go to the lights at the top of Grosvenor Road where you must turn either right or left - go to the left (you are joining the city centre one way system).
At the next junction (you'll see a statue known as the 'black man' in the middle of the road), you are turning to the right, so will need to get over to those lanes signed to turn right onto Wellington Place. Head straight down, right past the front of the city hall (on the right), onto Chichester St.
At the bottom of Chichester St., you have to go left onto Victoria St. position yourself to the right and head straight down, past the Albert Clock, down to the next major junction where the road veers to the right as well as heading straight on - you are veering to the right onto Waring St.
Keep right (don't end up in the lane for the Queen Elizabeth Bridge) and head to the next junction (top of Anne St.) go straight on. You're heading for the Waterfront Hall. You should be seeing signs for Central Station now, and the access to the carpark is left at the smaller junction just after the Waterfront, and follow the road after the roundabout (Lanyon Place & right onto Mays Meadow). You'll know when you're there because you will arrive through the underpass and see the NIR signs as well as Maysfield Leisure Centre.
All this sounds like a long way, but its not so be ready to jump your lanes when you need to.
Hope that's helpful.