Some google search should give you this guide which looks a quite OK procedure, or you can use a custom firmware such as the one available in our forum which comes already rooted.

From what I remember (my Cube U30GT-H is broken at the moment) you should know which Cube U30GT version you have by looking in the Settings / About tablet, the full model name should be listed there. The H version is newer and has some minor changes in hardware that make it incompatible with W version.

Cheers.

The guide I mentioned in Post #2 should really help, you'll just need some spend some time understand the terminology and trying to figure things out.

In addition we also have a guide for ADB setup here: http://www.arctablet.com/blog/devices/arnova/adb-and-fastboot-tutorial/

You'll just need to stop when you get "adb devices" command working, as, like globula commented, there is no fastboot on the Cube.

Cheers.