0.4 => 0.5
(and 0.5 versions updates) Two cases :
Cat is not customized a lot : the most simple is to disable ACS plugin with the small icon to delete all ACS variables (in plugins administration page), and to re-enable ACS plugin.
if your ACS model Cat is fully customized, as many components changes with 0.5 version, you must insert components in Modules. This can be done in administration area, page by page and Module instance by Module instance.
0.3 => 0.4
0.3 was the first ACS release. Migration of parameters was NOT automated. Please go to administration interface, display all variables, and copy/paste this part in a text file. So, you get a backup of your 0.3 configuration values. After the upgrade of ACS from 0.3 to 0.4, you can configure new 0.4 components with old values.