1. Do it from a LiveUSB
2. Move the small partitions out of the way (to the front of the disk)
there's a small chance your bootloader won't work anymore if you move the /boot, just keep a liveUSB ready, it should be rescuable with a few magic mounts, chroot, and a grub-install (or whatever else you use)
that said though, make sure you don't have anything important on that disk in case shit fucks up, the usual
2. Move the small partitions out of the way (to the front of the disk)
there's a small chance your bootloader won't work anymore if you move the /boot, just keep a liveUSB ready, it should be rescuable with a few magic mounts, chroot, and a grub-install (or whatever else you use)
that said though, make sure you don't have anything important on that disk in case shit fucks up, the usual