You need to shrink it down, 2.4MB is way too big for an avatar.
Just open it in paint and click on resize - change to pixels and then make it 300x300 and then save.
The forum should be fine with that.
It will resize but I did limit because we're already at 9GB of data, no reason to take up 2MB for a 150x150 avatar
It doesn't downsize the file, it just resizes it to fit. Lots of wasted storage for tons of avatars if they're all 2MB.