There is a screw holding the bumper on in each wheel arch. Remove these. Now look under the car and you'll see loads of those plastic clip used to hold plastic trim together. Use a flat blade to pop them out. Open the bonnet and you'll see plastic trim around the top edges of the engine bay. You want to remove to plastic strip at the front of the engine bay. Pop the plastic clips out and jiggle that bit off, navigating it around the bonnet latch.
Now, just carefully (but with a little pressure) start nudging and tugging the bumper off. Start at one side, in the wheel arch and go around. If you detect any resistance then stop and trace the resistance. It's likely a left over clip you've missed. Don't tug too hard as you don't want to damage or snap anything.
It's super easy. The first time you do it, it takes about 20 minutes, but I've done it so many times I can have the bumper off in under 5 minutes these days!