The "CLI Reference Guide" can be found on InfoSight. Once you login to InfoSight, click on the download icon in the top right portion of the page. Under the "Nimble OS" tab, select your software version and then select the "CLI Reference Guide" below. In this document, you will find the commands needed to manage your array. The information you are looking for will probably be in Chapter 36 (~page 259.)
If your snapshots follow a specific naming scheme you could use the snapshot collection list to find the ones you want to remove. For example the following line will find all the snapshots that are in the VMware volume collection that have the keyword "hourly" in the name. It then reverse sorts the snapshots based on the date in the name from newest to oldest and only shows the ones after the first 15 lines. Then the tr and cut commands show just the snapshot name.
Nimble OS $ snapcoll --list --volcoll VMware | grep hourly | sort -r -k2 | tail -n +15 | tr -s " " | cut -d " " -f 2 VMware-hourly-2015-06-17::19:00:00.000 VMware-hourly-2015-06-17::18:00:00.000 VMware-hourly-2015-06-17::17:00:00.000
This can then be used in a for loop to remove those snapshots.
for x in `snapcoll --list --volcoll VMware | grep hourly | sort -r -k2 | tail -n +15 | tr -s " " | cut -d " " -f 2`; do snapcoll --delete $x --volcoll VMware; done