Need to upgrade from 100 amp to a 200 amp main breaker
Unless you're running all that stuff at once I don't see why you need more than the 120 amps you have... If you buy a Kill-a-watt device you'll find that audio, video, and computer products never draw nearly as much power as they're rated for. I think my Dell, with it's 400 watt power supply, along with the monitor, draws 50 or 60 watts.
Maybe what you need to do is run a new circuit to the theater system.
Anyway, if you do need to upgrade your panel, here's the basics:
You get the power disconnected at the pole and get the permit.
You get new supply lines if yours aren't big enough (probably not).
You get a new meter base if yours isn't modern (needs a grounding lug).
You get a new load center.
You pull out all the breakers, and carefully remove the wires from the old load center. You replace the supply lines and/or meter base if necessary. You put in the new load center and replace breakers and wires.
The new load center may have terminals in different locations, which might require new supply lines between it and the meter base.
Mine cost about $600 in parts. I didn't do it myself, but I assisted in various ways.