Is it easy to replace the brake light bulbs? 
also I have condensation in just the rear left plastic light lens assembly? 



Which bulb are you trying to replace? The brake lights are LEDs on those if I am not mistaken. 

To replace anything on the tail light the assembley needs to come of the car. Open the trunk, remove the black liner and the tail light bolts will be exposed. 

If you have condesation, you can remove the tail light and inspect it for any cracks. Also check where the cable connects to the tail light to make sure it is not loose. 

If you still have condesation, you may have to replace that tail light. A used one would work just fine.