Catalina to Sanoma help

Hi everyone,
I have a 2013 iMac running Catalina. About a year ago I installed Ventura on a separate partition using OpenCore Patcher, but I’ve still been using Catalina as my main system since then.
Unfortunately, Catalina is getting less and less supported, so I need to move on — I’d like to install Sonoma now.

How should I go about this? Is there a tutorial for this process somewhere?
Can I safely delete the Ventura partition, or could that damage the other partition somehow?
I’m worried about losing data. I do use Time Machine, but I’ve had cases in the past where the backup wasn’t usable.

Thanks a lot for your help!