To change your time signature, Go to Option/Project General Settings
What you need to change is the Bar Length and the Beat Length. Nromally, the Beat Length stays at 4. As for the beat length, if you want a 4/4.. well leave it as it is. that's the default setting.
For a 3/4, put the bar length at 3. That means that there will be 3 beats in 1 bar. Actually, 3/4 is really stiff (in my opinion) so I'd suggest 6/4 instead, at a higher BPM (speed).
Now, thing is, making a 3/4 hiphop track is nice, but the sound will be strange, unusual... I dont know many hiphop tracks with a 3/4 time signature. But the to have an idea of what it sounds like... in a 4/4, if you count the bars (1, 2, 3, 4, 1, 2, 3, 4...) you normally have a kick at 1, snare hits at 2 and 4 and the rest depends...
in a 3/4, count 1, 2, 3, 1, 2, 3... a kick at 1 and a snare at 3 and the rest is up to you...
My guess is you wanna make a 3/4 since you read the heatmakers use 3/4 drums... if that's what you're aiming to have, just remember that their drums are REALLY busy (lots of things happening on the beat, lots of kick hits and some sparse snare hits here and there) and that they are at on double the speed of a regular hiphop track... like 170 between 200 BPM. Experiment and you'll find the sound you're looking for, but dont forget to have at least a kick at 1 and snare hits at 3.