Before doing anything with your hard drive you should boot into your Windows partition and run disc cleanup and disc defragmenter, this will help to ensure the partitioning process will run smoothly, ignore this advice at your peril! Having said that, if you plan on removing Windows and just replacing it with a Linux distribution, the previous steps can be bypassed, in fact the whole partitioning section could be bypassed and you could move straight to Installation and the Installer would remove Windows and install Linux in one go.
The first thing to do is prepare your hard drive. This can be done using a Windows application for hdd partitioning, but I will be showing how to do it from the live-cd prepared using the "How to create a live-cd / usb" page
After booting into your live-cd (or usb) you can access the program "GParted" from the main menu -> Programs -> Accessories -> System -> GParted
You should be presented with a screen something similar to the first image. Your own drive may have just a single partition, this is also quite normal and you can just follow the instructions to safely resize your main partition.
Start by selecting the partition you want to resize, in this demonstration it is the second partition which was used for data, and will have minimal impact on the current Windows system. Next right click on the partition and select "Resize/Move", this will bring up a dialog box like the image here.
Here you can either enter the "free space following" to read 40960 (40Gb) or whatever space you have free(I would recommend an absolute minimum of 12Gb), or use the right hand slider to visually resize the partition. You can install using less hdd space than I have recommended, but you will soon run out of space when you start using the system and installing a few packages.
Once you have set the required space settings click on "Resize/Move" and you will be returned to the main GParted screen. At this point nothing has actually been changed, but is simply set to do so. If you are happy that the settings are all correct click on "Apply" (the tick in the main toolbar)
This will write the changes to the partition table and when finished you will have a blank space in your partition table of 40Gb, you are now ready to create the Linux partitions.
At this point I will have to let you know that there is a limit of four primary partitions allowed and some of you might have three partitions already and will need to create an "Extended Partition" as the fourth "Primary" partition to allow for more partitions to be created. The procedure for this is quite straight forward, simply create the free space in the same manner as previously instructed, or if you have already cleared some space simply right click on the empty space and select "New". This will give you the option to create a partition and the type etc... Create a partition with all the remaining free space and select the type as "Extended Partition", click apply and you will now be able to create more partitions in this "Extended partition" area.
Your partition table should now look something like the previous image, with free space at the end of the partition table. Now we can create our partitions to house Linux. Right click on the free space and select "New" and create a partition of 4096 Mb (4Gb) and select the type as "linux-swap" this is an area of your hdd that will be used for swapping running software from ram when the system requires more resources. I would not advise setting up any system without adequate swap space, even Windows uses space on the hdd for this purpose and Linux just has a different way of implementing it. Next create another partition using the remaining free space and select the type as ext4, this will be the partition that the system will live on.
Click on apply to write the changes to disc and when that has finished you can close GParted and begin installation.
Now you are ready to install Q4OS using the instructions HERE