I have the version Blocks v.2.6.2.
When I start the update it does not work, it says: “Can’t make a temporary directory for the update download at /Users/…/Library/Caches/com.Blocs-2/Sparkle/Blocs 202”
I would like to go to the new version 3 of Blocs which will be available in the next days, but I think that I must first update my version to v2.6.5
I would try deleting Blocs from the apps folder and downloading the trial from the home page https://blocsapp.com. It should automatically recognise your license.
The current version of Blocs is 2.6.4, but I don’t see why you would specifically need that for an upgrade to Blocs 3.