You can use the Snapshot Manager to delete snapshots for a virtual machine.
When you delete a snapshot, the changes between snapshots and previous disk states are merged. All the data from the delta disk that contains the information about the deleted snapshot is written to the parent disk and merges with the base disk.
Deleting snapshots involves large amounts of disk input and output, which can reduce virtual machine performance until consolidation is complete.
The time it takes to commit or delete snapshots depends on how much data the guest operating system has written to the virtual disks since the last snapshot was taken. The required time is directly proportional to the amount of data (committed or deleted) and the amount of RAM allocated to the virtual machine.