In general, the update process is simple, you need to overwrite the files and run a script to update the database, but there are still some points that should be discussed in more detail.
And so the first, the basic version of the program and the Extension are related. If you have an Extension installed, you have to update Extension too.
If you have just purchased Extension, but your are using the old version of the app, then before installing the Extnesion, you have to update app to the latest version.
Now let's consider the situation when you use a very old version of the program, for example, 1.8 and you need to upgrade to 2.2. In this case, you need to overwrite files from the new version of the program, since the installation archive of the program already contains files for updating the database from previous versions. And so, overwritten the file from the new version and then go to the archive of updates to version 1.8 and perform only database updates.
Please note that sometimes when updating, it is necessary to run scripts to correct the data, therefore, carefully follow the instructions for updating.
Then, after running all the scripts, switch to version 1.9 and also perform only database updates. And so consistently up to version 2.2.