The following steps are recommended:
1) Back-up
Back-up all your files. This is always recommended in case critical files get deleted or overwritten by accident.
2) Un-install
Log-in to the Admin section and un-install the plug-in. This does not have any consequences for existing orders. This step is purely for the database.
3) Upload
Upload the files of the new plug-in and ensure they go inside the correct directory. Overwite the old ICEPAY plug-in files if prompted.
4) Install
Log-in to the Admin section and install the plug-in. This will ensure the database is up to date with the plug-in files.
5) Configure
Configure the ICEPAY main module and save. Ensure all the Status codes are unique.