You could look for files that you don't need in the backup and try clearing it up from inside.
Once you've gone down the 2MB limit try uploading it again and see if that helps you.
Also, I didn't encounter any too large backup files that I couldn't upload, but you can do it through WinSCP software. Upload your backup there and then use sysupgrade -r BackUpFileName.tar.gz to restore from the backup you've just uploaded. This should go past the 2MB limit.