Comandos Snap:
sudo snap find : To list the available packages
sudo snap install <package name> : To install a package
sudo snap list : To view all the installed snap packages
sudo snap changes : To view a list of logged actions
sudo snap refresh <package name> : To upgrade a package to its latest available version
sudo snap remove : To uninstall a package
Então, no seu caso, use:
sudo snap find pycharm : to get the version available
sudo snap install pycharm-community : to install that version listed
Use --stable, --candidate, --beta ou --edge para escolher a versão. (O padrão é --stable.) Exemplo:
sudo snap install --beta pycharm-community