Snapshots remain in your account until you manually delete them. To delete a snapshot from your account, in the control panel, click Images in the main navigation, then click Snapshots to view all snapshots in your account.
Snapshots are separated into two lists: one for Droplet snapshots and one for volume snapshots. To remove a snapshot, open its More menu and click Delete. In the confirmation window that opens, click Delete Snapshot to permanently delete the snapshot.