How to safely delete a system partition?

I got the following disk sda9 contains a new Linux installation which I'd like to keep, while sda5 is the old installation which I'd like to **free** (and successively merge with sda4, but we don't care). sda4 contains a Windows installation which I'd like to keep. The question, made to be sure of **avoiding (grub) problems at boot**, is: *do I need just to delete* sda5 *without any other operation, and nothing will break ?*