Yep, you can delete your Windows partition once you no longer need it or any data within it. Then once you update your bootloader (usually GRUB, some distros do this automatically when updating the system), Windows will disappear from the boot options.

Then you can either create a new partition in its place to store data on, or extend an existing partition to fill the empty space.

I'd recommend also backing your data as a precaution in case something goes awry.

Just one piece of warning for dual booting, if the EFI portion for Linux and Windows is on the same drive Windows could decide to nuke the Linux bootloader with any update...

It's not too difficult to create a redirect to the windows bootloader in Grub or similar, which is the solution I went with in the end.