If there’s no second floor then there’s a chance they’re not very structurally important. Usually roofs are supported by the exterior walls if you have trusses and a straight forward roof, if your roof has hips and valleys then there’s a good chance they’re needed. I’d be very concerned about the weight of the A/C unit. They’re more likely in place to support that weight, if so can you move the A/C unit?

Everything can be changed. If they’re load bearing then you’d have to. Put in a steel I beam and transfer the load to the exterior walls. This would need an engineer to design, but it’s not impossible. We have a house built in the 50’s with a second floor and had the main load bearing wall removed to open up the main floor. It’s possible, but don’t expect it to be cheap.