Windows users may need to resize a partition in order to install a dual-boot system and free space for a GNU/Linux partition.
Make a complete backup of your data. When your backup is finised, disconnect the backup for the computer.
You should be aware that resizing partitions is not a normal daily maintenance task. This is an exceptional tool, which can fail and make your desktop system unusable. Preferably, you can also by a new hard disc and avoid partition resizing.
You should free at lease 20Mb for the system and 25Mb to store movies, which is a minimum.
Start a normal live session.
Unmount the disc that would like to resize. Right click on the disc and select "Unmount". You cannot resize a disc which is mounted.
Run gParted: in System menu, Administration menu, select Partition editor.
In gParted windows, select the partition that you wish to resize.
In Partion menu, select Move/Resize:
Move partition borders to resize the partition:
When done, click on Resize/Move:
When done, click on Apply changes.
Wait until your changes are fully applied. Depending on the size of the partition, this may take a long time.