Whether the snapshots can safely be deleted mainly depends on how the VM's virtual disks have been provisioned, and whether it's done with the VM powered on, or off.
In case of thick provisioned virtual disks, snapshots can be deleted (using "Delete All", and the VM bring powered off) with almost no requirement for additional free disk space.
Deleting the snapshots while the VM is powered on, or if thin provisioned virtual disks are used, will require temporary disk space, where the amount depends on different things.
If you want, then run ls -lisa > filelist.txt from the command line to list all of the VM's files, and attach the "filelist.txt" to your next reply. This will then respond with possible options.
André