1) You can go to your file
2) Duplicate another new file with your existing one
3) Then flatten all the layers from your new duplicated file
4) Click 'Image' & look for 'Image Size'
5) Adjust to the file size by either reducing the pixel size/resolution size or both to achieve to the file size mentioned previously.
Don't know it works or not cause I don't even have my own avatar. Hee...hee...