No, you cannot shrink snapshots. However, do you really need these 4 snapshots? As a best practice, snapshots should only be kept as long as necessary. Keeping snapshots for a long time will consume considerable disk space (as you can see) and may also decrease the VMs performance.
To delete the snapshots open the Snapshot Manager and run "Delete All". Remember that due to the size of the snapshots, this may take a few hours.
André