Scratch

I'm new here on the forums, although I've been playing around with the program every now and then for a few months. Now that I'm finally starting to get good ideas for programs I could make, I thought it was time to get an account on here, so here I am. I'm usually pretty good at figuring things out on my own, so I only really have a few questions. I can't seem to figure out the size requirements for profile pictures (avatars). The image I'm trying to use is 140 kb, and I'd like to know how much smaller it has to be before I can use it. Thanks in advance! (Since I couldn't post in FAQ's, and it's not directly related to the Scratch program, I decided the best place to post this would be here.)

Also, does anyone know a way to deal with the lag you get when you have a really long script on one sprite? It's starting to bother me, but I have a long way to go on my program, so I'd like to know if there's anything I can do about it.