Try gparted on a liveUSB, you don’t wanna modify the partitions you’re actively using because it can(read: will) result in data loss.
If you’re willing to spend a little bit of time on it and actually know what’s happening behind the scenes, read the man-pages for fdisk and do it manually from a TTY, but for cereal, use a liveUSB and ffs do NOT mount the filesystems first