How to remove older volume snapshots

[Venkata Suneel Babu Mallela]

Hi All,

CloudStack Secondary Storage is reached 94%. The retention policy is as below,

Daily                      -              Keep 7
Weekly                 -              Keep 4
Monthly               -              Keep 8

Snapshot.delta.max       -              16

Can anyone suggest, How to remove the older snapshots which are not showing in 
CloudStack UI?

Thank you,
Suneel Mallela