I bought some new drives to replace the old ones I had lying around, and want to replace them entirely (4x 1tb -> 2x 4tb). I have a few apps running on it (Syncthing, Transmission, Tailscale, etc.), and I wanted to know what the best way to perform a drive upgrade would be. AFAIK the apps are installed on the pool as well, so will I just have to reinstall them from scratch?

The motherboard has 5 SATA ports, which are all currently occupied, so I don't know if I can do an "in-house" replacement.