You do not need to uninstall the extensions before updating them. In fact, by uninstalling them, you will lose all configurations (module instances...).
Before updating, make sure you read the change logs and are aware of potential backward compatibility issues.
Cached scripts and styles are removed on update. Updates fix issues, add features and/or improve performance and these wouldn't be reflected unless all cached files are re-generated.
Migrating to v2.2.x from v2.1.x
Layouts and module/view templates have been modified. Although these changes won't break your pages, you will need to update your overrides, if any to get the latest functionality and fixes.
Stylesheets have been modified to better fit your templates and allow for better responsiveness as well as using new techniques for display (flexbox).
The dash after the hits has been removed from the stylesheets, it is now a parameter called 'separator'.
Migrating to v2.1.x from v2.0.x
The caching of stylesheets and scripts has gone through a total rewrite. It is no longer necessary to change file permission access on websites that have very tight security rules. If you have setup file permission access for the files of this extension, you can now safely remove them from your server configuration.
You may still, however, run into access permissions under the new caching system. In that case, it is just a matter of granting access to (or
/cache folder created for the extension.