I had a 'domain' called APP03. I was performing auto snapshots each night using /usr/bin/virsh snapshot-create APP03
I then wanted the domain to be called APP01 for clarity's sake, so I did virsh dumpxml APP03 > APP03.xml, edited the name to APP01 and changed the ID. I then did virsh define APP03.xml to get APP01. 

I have now realised that the qcow2 images are huge (1.1TB image but 80G inside the virtual machine), I am assuming this is the snapshots tagged onto the virtual hard disk? 

How do I reduce the size of those back to something realistic? I've removed old snapshots from APP03 using virsh snapshot-delete APP03 '<snapshotidnumber>

Hope this makes sense