They mean the same thing, essentially. However, the first sentence indicates there are many things at the moment that the speaker would want to do, while in the second sentence, the speaker feels that having more time is something they might have in the future, not now. Hope this helps, Shinji :)

A difference does exist if you are determined to find it: Sentence #1: Right now there are many things I want to do but I cannot do them because I don't have enough free time. Sentence #2: If at some point in the future I have more free time, my desire to do things would, at that future point, increase and I would discover many things I like to do.

The meaning is the same, but a grammar professor might have an opinion on which is better. Normal people use both versions in conversations. Good luck!