Customizing your Grub2 config by hand is not a trivial task. On a re-purposed desktop over the past couple of months I’ve installed a bunch of different OSes, and my Grub menu on boot is a mess to say the least.
After installing more than one bootable Linux, you also (unless there’s a workaround for this?) end up with each Linux having it’s own grub config (/boot/grub/grub.cfg), although only one (the last installed) will have installed it’s config to your MBR. There’s a good question/answer on this here. In my case I do have two Linux installs, Mint and Kubuntu, so I did have to look at the config of each and work out which was currently installed to the MBR before I started doing any editing of the configs.
Luckily there’s an easier way to customize what OSes you have in your menu, using Grub Customizer – for install and usage see post here.
Part of my mess is having a prior install of Vista, upgraded to Windows 8, and then later upgraded to Windows 10. The boot menu options left behind are now for some reason a mix of all 3, even though only Windows 10 is actually installed and bootable. Plus I have a few Linux distros too:
Switching to View/Show Hidden, you can uncheck the menu entries you don’t want displayed, so that’s an easy fix. There’s plenty more options to configure and customize too, but for simple menu housecleaning, it’s an easier option than attempting to edit the grub config files by hand.