The Correct Way To Resize In Place
qemu-img resize kvmuserwindows2008dcetest.img +1G
Below is a common mistake that some users make they are trying to specify a new image name but it can be resized in place (just make sure the VM is NOT running and you've backed up the data in case something goes wrong).
qemu-img resize kvmuser453111.img kvmuser453111-larger.img +5G
New image size must be positive