My first step was to find out how to get the updater working again. The problem has been solved.
But now the question for me is, can I update my currently running e/OS 1.14 system to 1.17 straight away or do I have to install the subsequent updates step by step?
Dear @KayPeters Welcome to the forum and welcome to eOS.
Updates within the e-ecosystem are always full system updates - therefore you can directly update from v1.14 to v1.17.
No step-by-step update necessary. Just give it a try.