How can you make a file so that it's less than 1mb???

So I attempted creating a complete mode track, but when I uploaded the image, it said that it was more than 1MB. How do I fix that???

I think there is some way to just use a link but what I do is make my own simple images (since my N64 wario stadium also used over 1MB)

Well if you're going to fix that use an image that is less than one mb

Eh ok.
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