Hi Atlantis,
Here's how I go about doing it in the Windows version of the program (assuming your song is in 4/4 time)...
1. Click on the bar I want to make 2 beats. Go into "Bar Settings".
2. Set the bar to 2 beats. OK out of bar settings.
3. Click on the bar following the 2 beat bar. Go into bar settings and set the bar to 4 beats. (If you don't do this, every bar after the 2-beat bar will be 2 beats.)
That should do the job.
In a 2-beat bar, chords on beats 1 and 2 are the only ones that will play. I've found it necessary to add a chord to beat 3 because, without it, Realtracks don't always align time-wise. It doesn't matter what the chord is on beat 3 because it doesn't play in a 2-beat bar.
Hope this helps,
Noel