Sometimes I feel really bad because I want completely new friends.
I hear you, for sure. Why does that make you feel so bad?
I feel it's not normal to replace old friends with new ones because I don't know them much in comparison to my old ones.
It's understandable to want new friends, but you shouldn't get rid of your old friends just because you want new ones. Try keeping both!
But I prefer the new ones to the old ones.
Even if you do prefer your new friends, that doesn't mean you need to get rid of your old friends. There isn't a limit on the number of friends you can have.