How to extend root file system

Newbie here. Using fusion 6.0.3 on an iMac running Mavericks.

Created a trusty tar vm using defaults. Ended up with a 20GB root filesystem.

Decided I needed more - was able to extend sda1 which root is mounted on to 40GB.

Can't figure out how to extend the root file system. I've tried using gparted - doesn't allow me to do it.

I assume I need to unmount root.

I tried booting from a live CD "try UBUNTU", that created another VM - from there gparted couldn't even see the file system on my original VM.

Help appreciated.

Thanks,

MRR