Hibernation is really only a feature to use on laptops / tablets. So DO NOT use this guide on a laptop or tablet.
Turning off hibernation automatically deletes the hibernation file.
The short version is this:
1) Open a command prompt
2) Type “powercfg /h off”
For the less quick or confident here are a few screenshots to help:
1) For Windows XP or 7 users Click Start then click Run (or hold down the Windows key and press R)
2) Type CMD in the Run Window
3) For Windows 8 or 8.1 Right-Click in the bottom left corner and choose Command Prompt
4) In the command prompt windows type
to get to the root of your system drive
to show all the files in the drive
6) If hibernation is enabled you will see a file called “hiberfil.sys” that is up to the same size as your RAM
powercfg /h off
to disable hibernation
to show the files in the drive again
9) You should see that the “hiberfil.sys” file is gone and you have gained more disk space
10) If there was no hiberfil.sys file in the first place you may not have been in your system drive, or hibernation was already disabled – running step 6 will do no harm if you want to try it to be sure anyway
11) Type Exit to quit the command prompt
While these days on a machine with TB of hard disk space a few GB might seem inconsequential, the hiberfil.sys file can often exist on virtual machines - Think of wasting 1 or 2GB per virtual machine! If you run a few test networks on the same system as I do it soon adds up, and you wonder where that 20GB went to.