Resize Boot Camp partition
Though grgarside's answer was the correct &amp; only correct answer at the time, iPartition is no longer the 'go to' app for this kind of task. It has unfortunately been left to languish &amp; can't handle CoreStorage volumes at all.

The only replacement - &amp; actually improvement - on iPartition is now Paragon Hard Disk Manager

It can not only resize Bootcamp partitions, it can fix them &amp; even back up or move them to a new drive without breaking anything else in the process.

Full feature list here - https://www.paragon-software.com/home/hdm-mac/features.html

no affiliation, merely a satisfied user.