Question about the file size for screenshots

I've successfully uploaded quite a few screenshots already but I've had some issues regarding the limit for the size of the files (2MB). I've been using a website called TinyPic to reduce the size by uploading the picture there first and saving it.

But even with that, the size of my screenshots are still usually slightly above 2MB or higher so I've had to crop out the bottom part of some of them to meet the size limit. Those screenshots were still accepted but I've just found out on the forum that doing so may be against the guidelines. I really want to strickly follow those guidelines but, right now, I have no idea how to reduce the size of my screenshots to 2MB or under without having to crop out the bottom or reducing the quality by too much (making them too blurry).

So, my question is: How do you guys reduce the size of your screenshots? I'd really like some suggestions.

PS: Without going through those steps, my screenshots are generally between 4-5MB, initially.