Plan

Current state

index	fs type	name	offset-size
0	-	free	0-1TiB
1	fat32	EFI	-
2	ext4	root	-
3	swap	swap	-
4	-	free	-

Step 1: new EFI partition

index	fs type	name	offset-size
0	fat32	EFI	256-1GiB
1	-	-	-
2	fat32	EFI	-
3	ext4	root	-
4	swap	swap	-
5	-	free	-

• Mount 0 (/dst) and 2 (/src).
• rsync -a /src/ /dst/
• Unmount 0 and 2
• Get GPT partition UUID of 2 with tool (fdisk, sdisk, gparted)
• Delete 2 (old EFI system partiton)
• Change GPT partition UUID of 0

Step 2: new ext4 partition

index	fs type	name	offset-size
0	fat32	EFI	256-1GiB
1	ext4	new-root	-
2	ext4	root	-
3	swap	swap	-
4	-	free	-

• Mount 1 (/dst) and 2 (/src).
• rsync -a /src/ /dst/
• Unmount 1 and 2
• Delete 2 (old root)
• Delete 3 (swap)

Step 3: expand new root ext4

index	fs type	name	offset-size
0	fat32	EFI	256-1GiB
1	ext4	new-root	-

profit