Add the repo as per the instructions.
apt upgrade
If you don’t like the current version, remove the repo from your apt list.
apt upgrade (you should probably apt purge crystal, but you can likely get away with the lazy way)
Downloading from https://github.com/crystal-lang/crystal/releases and uncompressing the .tar.gz is the easiest way for me. But my use-case is sporadic usage of old versions. As long as you prepend the bin directory into the path you should be good to go.
Gonna add my two cents, just use a version manager. I use asdf which has support for Crystal and several other languages. If you need a specific version of Crystal it’s super easy to just do asdf local crystal 0.29.0
Just installed asdf (similary to rbenv I think), super easy indeed.
Installed both version and switched between them to run my tests.
Thanks for your 2 cents.