Compressing 5.2Gbs to 4.7 or less

Hi, I have this ISO compressed with .rar and it’s at 4.7 but it’s a few bytes over so I can’t burn to a 4.7Gb disc, any idea how I can compress the .rar file or any idea on a different compressing type?

You can try maximum compression settings in WinRAR or the 7-Zip format. What purpose would that disc serve?