It's not rocket science, but I did install AC for about 8 years.
If you have a place that's California style ( no basement, air handler in attic or closet, split system with outdoor heat pump), you are limited to adjusting by closing down louvres at the register in hot room ( assuming you want to heat cold room) to try to direct heat to cold room.
Some of these fast built tract places had poorly designed or installed systems. Somebody competent could alter things a bit at the plenum ( preferably in an attic). Sometimes there are dampers at the plenum ( usually shitty ones), they may be covered with fiberglass insulation, look for a little metal arm about 3 inches long, turn it on the duct leading to hot room.
It's much easier on Eastern style with hard ductwork and basement installation.
A plenum is basically a metal box that the output of the FAU ( forced air unit) flows into, if it doesn't get distributed ( balanced) from there, you get hot/cold sections of the structure.
It might be worth a few bucks to balance it, I make alterations and stuff to systems for friends, add a vent here and there as needed, but you really have to see it. Shouldn't cost a bunch to find somebody to fix it.
If you have something like figure A, you should be able to do it yourself. That's what I call Eastern style, Western style... you could just have a poor duct plan, bad install job, etc.
I don't like duct cleaning services, they can destroy that cheap flexible ( non-metal) ductwork.