If you are on v2.3.5 or lower, first update to v2.4.0 - Download 2.4.0 package. Once you have updated to v2.4.0, update to the latest version using the link below.
If you are on v2.4.0 or higher, update to the latest version - Download latest package.
Step 2: Unzip the downloaded file
Step 3: Upload the Unzipped file to your [IWP] folder, and also overwrite all files.
Step 4: Run this file in your browser - http://youriwppanel/updateManual.php
Note: Make sure you delete updateManual.php after you are done with this process. (Its located inside the IWP folder)