Everything worked out, it was relatively easy:
1. Downloaded Clonezilla Live as a ZIP file from Clonezilla live and flashed it onto a USB stick. Booted Windows PC from this stick and copied the old SSD to the new SSD.
2. Downloaded Gparted Live as a ZIP file from GParted -- Live CD/USB/PXE/HD and flashed it onto a USB stick as described. Booted Windows PC from this stick and enlarged the partition.
I probably could have cloned the SSD with another program, but I didn’t want to risk it.
And this one makes me think and I decided to no longer keep my Lightning node running with the current amount. I will heavily reduce it and provide only a BitCoin Core Node to the public:
https://community.umbrel.com/t/how-to-access-my-wallet-if-my-raspberry-umbrel-breaks-up/23553/3