I'd say to copy all of your main Home folders in Ubuntu that has content (about 7-8 folders total) to an external of some type (USB stick if not too much is fine), and start over with Ubuntu 16.04 clean. You can copy those folders back with content, by deleting any with the same name on the new Ubuntu install. It's a drag & drop operation. When you reinstall, you can plug the external in, see what you have, and delete the folder in the OS bearing the same name, and copy yours over, one by one. No data loss.
Windows 10 doesn't require much space either, though you should also create a Data partition for that OS to prevent against loss, by shrinking the OS partition (80-100GiB is plenty for 'C') from Disk Management within Windows, being sure to run a couple of defrag passes first. Then when booting with the new Ubuntu media, create how much you wish for Data, making it a Logical partition. Be as generous as you feel you need with Data, with a 1TiB HDD, you have tons of space. Then install Ubuntu 16.04 fresh, making sure that root or '/' is no more than 40GiB & Logical, if you're not Hibernating, then 1024MiB Swap is good, if you are, then make it the size of installed RAM. Then use the rest for /home, which should also be Logical. Unlike Windows, Linux distros runs fine on Logical partitions, but Swap will make itself your last available Primary.
By chance, if your computer was sold with Windows 8 or higher (you'll have UEFI Firmware rather than BIOS), you can convert the HDD to GPT with GParted Live, or any partitioning CD, then you'll have unlimited primaries, though would have to install W10 clean, something you may not want to do, especially if running fine. Since you didn't say, just letting you know to cover the bases. Note that GPT partitioning of a boot drive won't work unless your computer has UEFI Firmware. If BIOS based (pre mid-2012 or earlier), forget it, most motherboards supports MBR partitions only.
And be sure to create a backup of Windows 10, including the 100MiB System partition, before a new Ubuntu install. In fact, you can create a Data partition for Windows 10 with the Ubuntu install media, it has GParted under Administration, just make it the size you want, and make sure than you select 'ntfs' from the file system drop list before formatting & click 'Apply All Operations' (the right arrow) & then install Ubuntu 16.04 fresh from there. You should make root as noted above small, because it doesn't need nor use a lot of space, 30 to 40GiB (30960 to 40960MiB) is plenty. That'll allow you to make /home (where your data is stored) as large as you need. It's your choice where you want to install Swap on a single drive, I choose in the middle of root & /home because that portion of the HDD is faster. Some may prefer it on the end to grow or shrink as needed w/out messing with /home if an adjustment is needed, that's up to you where to place Swap.
Hopefully, this is of some assistance, the point being, make Windows as large as needed, including a separate Data partition to store files. In fact, you have lots of space for Data, just remember to make it a Logical partition. Plus before installing Ubuntu 16.04 (recommended), be sure to be signed into your browsers, to keep your bookmarks & extensions as is.
Good Luck & let us know if we can be of further assistance.