Sorry about the delay, got distracted making sure my daughter made the bus. As others have been saying I don't know how much of this will be necessary, because at least in theory it should push back. Modification usually results in a little difference in size, but rarely a large amount. Clearing space isn't really a bad thing, so you may need this down the road anyhow. So without further ado...
You don't have to ditch the theme, there are ways around this. The easiest way if you like the theme, is to clear out some of the unwanted ringtones. I assume they are still there, it has been a while since I ran that combination.
You may want to make a backup, just in case something goes wrong.
If you have something like root explorer, it makes this process a little easier. You can browse to /system/media/audio/ and browse through the folders there and get rid of a few of the files. You shouldn't have to get rid of too many to accomplish what you want to accomplish, but if you want to spring clean go for it Be careful though and not delete one you wanted. You can listen to them from there by just tapping on them. Remember you will need to set the /system partition in RW to remove the files by clicking the top right hand button.
If you don't have a file manager, you can do it through command line, but it isn't going to be as quick.
Basically what you will need to do is something like this.
ls = lists files and folders in the directory you are in, in this case the ringtone folder. The -l isn't necessary, but it shows the sizes of the files, which in this case may be helpful in your decision of which ones to trash. Also, in this method you will have to use the ringtone browser on the phone to listen to them (not really a big deal though).
Know that you can cd /sytem/media/audio/notifications/ and cd /system/media/audio/alarms/ for more audio to remove.
You can then, mount the system rw, and rm the file.
So in a mock run of what I would do in a command line deletion.
The reboot and sync probably aren't necessary.
mount -o rw,remount -t yaffs2 /dev/block/mtdblock4 /system
mount -o ro,remount -t yaffs2 /dev/block/mtdblock4 /system