An easy way to do it is with WinRAR. Install it, then right click on the ISO and choose "Add to archive..." (which will be an option once WinRAR is installed). On the screen that pops up, you can give the archive a name, choose whether you want RAR or ZIP files, set the compression level, and you can also split the file into multiple RARs using the "Split to volumes, size" drop-down list, bottom-right.

There are a number of presets, once of which is 100MB, so if you choose that your RAR will be split into 100MB chunks, or you can type in a value yourself and select either bytes, kilobytes, megabytes or gigabytes from the list to the right, so typing in 95 and then selecting MB will split the RAR into 95MB RARs for example.