I tried updating it via iTunes; I made a back-up which seemed successful, now I tried for the update and then it gives me the following message;
iTunes could not back up the iPhone "iPhone van <my name>" because the backup was currupt.
Delete the backup for this iPhone in Devices Preferences, then try again.
The back-up (of pictures/photos) was successful, so far I can see, I do not know where to find 'Device Preferences' to Delete the backup, also I was not aware that during the software update iTunes would automatically make a back-up, if I'd known that I wouldn't have made a back-up myself before that.
Mind you; I am ONLY updating to 9.3.6 due to the fact that I want to UPDATE my WhatsApp on this phone, before activating a new SIM-card and starting to use a new phone (I know my WhatsApp has not been making frequent back-ups lately and I do not want to loose 1+ years of messaging history).
Thank you for your help and assistance!