thanks very much guys.
Issue is still occouring tho 
ruby /vazr/www/discourse/vendor/bundle/ruby/2.6.0/bin/unicorn -E using 98% CPU at the moment , Forum unavailable
number of images , not sure what you would term an aweful lot - there are quite a few, but we are not a huge forum. df showing 80% of the 50GB used, on the admin panel in discourse it shows 5.7GB upload
the dovker update command I tried didnt appear to do anything, I have found instructions on how to install on Ubuntu 18, but not update… should I be following install directions?
prior to reboot of droplet this morning there were no convert processes showing, after reboot there are now 5.utilising approx 50% of cpu and RAM, rest appears to be in use by Ruby, Sidekiq processes intermittantly using resources, procesor and RAM still getting maxed out all the time.
Convert processes still getting killed due to being out of memory
Do we think there is still a queue of work being done - would a furtehr droplet resize help get through that queue? Forum still only staying online upto 30mins at a time, often shorter.