Easiest way would be to resize your existing image to a smaller size, then use the resulting free space to install your new OS. You can then edit your new deployment's configuration profile to add the new disk image, then mount it.
You can use df -h to figure out how much space you're using:
Code:
$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/xvda 8.8G 5.7G 3.1G 65% /
varrun 250M 56K 250M 1% /var/run
varlock 250M 0 250M 0% /var/lock
devshm 250M 0 250M 0% /dev/shm
In this case, I can resize down to 6 GB (~6000 MB), leaving about 10 GB for new stuff.
If you're packed to the gills and can't shrink your filesystem far enough, you can also add some extra disk space on the Extras tab and remove it when you're done.
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