Hello rsnow, welcome to Seven Forums!
You can use the Partition Wizard Boot Disk (PWBD) to do this shrink but don't take it to less than 100GB to be on the safe side and be sure
to use the boot disk and not the installed version.
Boot the PWBD and it will setup automatically without any input needed, right click the C: partition and select Move/Resize, then see the snip below for the next steps, then Apply and accept the final conformation.
Have a look at this tutorial at the link below for some other ideas and be sure to post back with any further questions you may have and to keep us informed.
Partition / Extended : Logical Drives
First download the PWBD ISO file to the desktop, be sure to get the PWBD and not the installed version; scroll down to see the download link for the bootable CD ISO file at this link below.
Partition Wizard Free Bootable CD
Then use ImgBurn to burn the ISO to a CD, at no greater than 4x speed with a verify; it was designed for use and works best from a CD rather than a DVD, then boot
the created CD to make the changes.
ImgBurn Free ISO Burning Software
click to enlarge