If you want to shrink yor Volumes in Windows 7, the avialable Disk space might be very small as of un-zeroed-out bits on your SSD.
To release those parts you can use sdelete from the SysInternals Tools (www.sysinternals.com)
On a command prompt type:
sdelete -c -s -z C:\
where “C:\” is the volume you want to clean up
PS: Also works great for Virtual Machine files (VMware & Hyper-V)
Hope this helps…