How hard is it to change the lenses and...
How hard is it to change the lenses and do I need any special tools?
You don't need any tools. It'll probably take you a couple times to get the hang of it and know what you're doing, but it's not hard after that. The main downside of lens changing is that you need to hold the lenses in a way that you're virtually guaranteed to need to clean them immediately after (via microfiber cloth, etc.). If you might be changing lenses daily for some reason, I'd suggest getting a second frame to minimize risk. If rarer -- like just every weekend, or every month -- it's not a big deal.
its really easy all you have to do is pop the old ones out and put the new ones in it took me 2 minutes to do it