Yes, there is a way to preserve a data partition while removing Windows 10 and its partition, but first, we must be very careful to do six things:
- Reboot your PC and in the BIOS/firmware settings, disable Fast Boot and Secure Boot. Different BIOS have different options, so I can't tell you precisely how to do that. After you have changed those settings, boot into Windows as you normally would.
- Make sure we know the drive letter and its partition number which has the data. We do this by running Disk Management from the Control Panel in Windows. Write down the partition number.
- Copy all data from C:, your Windows System drive letter, to your data drive. Things like files in and under C:\USERS\yourusername\APPDATA\ contain browser configurations including passwords and bookmarks you may need again. Also copy all the data in the Quick Access locations to that data-only partition,
- When you've confirmed that, make a backup of the data anyway, because disk partition changes can be tricky, and one small mistake can lose data forever.
- Make an Ubuntu LiveUSB (or Lubuntu, or whichever flavour you want) LiveUSB.
When you are absolutely, positively, done with Windows 10, then click on the windows button, click on the power icon at lower left, and while holding down the Shift key, click on Shut Down. This makes sure all changes are written to disk and the disks are released.
When 1-6 are done, then you can install Ubuntu / Lubuntu / *buntu. When it asks where to put Ubuntu, you choose Something Else and specify to put *buntu where Windows was, while not changing the other partition where your data is.