docker image cleanup before upgrade

Hi there. We're about to go and upgrade to RMv6.2 but I wanted to clean up our server beforehand.
Have reviewed How To Remove Unwanted Docker Images however how to you know/confirm the older resmgr_5.x are not being referenced and ok to remove?

A quick check shows we have alot of older images for resmgr:

#docker images | grep resmgr | wc -l
836

#docker images | grep resmgr | grep latest​resmgr_6.1 latest 371c6daa15ab 5 days ago 3.06GB
resmgr_5.2 latest 06db1ec147de 18 months ago 1.68GB
resmgr_5.1 latest 129f598f183c 2 years ago 2.18GB

[root@lpptzencc01 ~]# serviced volume status
Status for volume /opt/serviced/var/volumes:

Driver: devicemapper
Driver Type: direct-lvm
Volume Path: /opt/serviced/var/volumes

Thin Pool
---------
Logical Volume: serviced-serviced--pool
Metadata (total/used/avail): 208 MiB / 17.91 MiB (8.6%) / 190.1 MiB (91%)
Data (total/used/avail): 194.8 GiB / 33.94 GiB (17%) / 160.9 GiB (83%)

6tbl4izbt1r84rkia29qtdui Application Data
-----------------------------------------
Volume Mount Point: /opt/serviced/var/volumes/6tbl4izbt1r84rkia29qtdui
Filesystem (total/used/avail): 99.99 GiB / 31.91 GiB (32%) / 68.08 GiB (68%)
Virtual device size: 100 GiB

[root@lpptzencc01 ~]# serviced snapshot list -t
no snapshots found
[root@lpptzencc01 ~]


Thanks in advance.