I have installed a new OS in the free space of the same hard disk after failing to upgrade the old one. Now there are two copies of boot partitions and EFI System partitions. After a harrowing experience deleting the partition containing the old OS where old swap is located, I am not confident to remove the rest of the partitions related to it.
Despite reading up Wikipedia articles pertaining to UEFI and GPT, I don't think I have gained sufficient overview of how the booting process works. Especially how the UEFI bootloader manages to find the correct EFI System partition (I have two) to boot up the new OS. Now I hope someone can enlightenment me on this issue so that I can gain some confidence and decide whether it is safe to delete the old boot (sda1) and EFI System (sda2) partitions.