my solar lights don't work anymore. i think it's the panels. Can I change them?

Sounds like your rechargeable batteries are dead. Replace with new rechargeable and let charge a good full sunny day before trying to replace panel.

Depends on how old the lights are. Solar panels are pretty reliable, I would suspect the batteries or the actual installation. If there is too much shade, the solar cells wont pick up enough sunlight to charge the batteries, and if it is cold, battery function goes straignt to hades. The batteries wont charge very well in the cold. I would try to replace the batteries with nicad batteries (that is what the originals are) or rewire the lights to work with a standard power supply. Since they are LED, they draw so little power they wont add much to your electrical bill. I wish you well with your project.

Before you jump to changing them (you might have a warranty/it is expensive), get them inspected.