It depends where your grub2 repository is installed.
And if your installation is fine, it will be on your boot partition (dev/sda1 for you). If it's not here, well I'll delete my post because you will have too learn how manage grub2 but i don't think that you want to. You can try rEFInd if you want something more easy to config.
So when you'll erase Ubuntu, nothing will append, except that when you try to run Ubuntu, you won't. And you will no longer have some command line access on it (I never use them).
If you want to remove the Ubuntu entry on you grub2, just find your
grub.cfg (probably there :
It will looks like that, then remove all section
Menuentry 'Ubuntu...' (not just the line).
If you install another Linux distribution, then be careful and copy your
grub.cfg (because it will probably be erased). Like this you'll be able to copy the Menuentry section for Window of your old file into the new one (don't touch your Window partition, or it won't be the same config).