How can I clear my computer disk space?

When I try to download something or just run some programs, a warning would show up and said that I have low disk space. The best effective way to clear my disk space/ How can I clear my disk space? Also, I wonder a simple disk defragmentation could be enough. Many thanks.
(Do I need to use a disk cleaner like Colorful Disk Clean? This program looks cheap and useful, or u guys have any other suggestions?)
This is the image of Colorful Disk Clean:

 

I would rather see a disk map from windows Disk Management than a third party app that costs $. There are plenty of free ones to try first if that's the way you want to go.
Go to Control Panel>Administrative Tools>Computer Management>Disk Management and post a screenshot of that. Then we can see what's really going on before you delete something by mistake.

 

@ Saker,

Disk defrag is not designed to retrieve lost disk space. It is designed to put the written files in sequential orders so that they can be read quickly and therefore improve the performance of your computer. It will not help regaining disk space.

As to issue of disk space.....
Did you buy a computer that comes with Windows 8?
or,
Did you upgrade your computer to Win 8 yourself?

If it is upgraded by you, your computer will have a folder called Windows.old.
It stores all the files etc from your previous Windows operating system. That file is huge.
Mine for example was over 20 GB.
If you have no use for it, it is absolutely safe to delete that folder. I did on mine.
The method is done via Disk Cleanup.
Here is a tutorial on Disk Cleanup ...........
http://www.eightforums.com/tutorials/2527-windows-old-folder-delete-windows-8-a.html

 

adding.................
While you are running the Disk Cleanup tutorial, there is also an option where you can delete all restore points except the most recent one. That will also regain a lot of disk space.
BUT, this has one drawback. You don't have any "old" restore point to fall back to.
So, don't do that UNLESS you are certain your computer is running smoothly and you do not foresee the need to do system restore for a while.
If you do decide to delete all old restore points, then make sure you create new restore point regularly each time your computer is running smoothly. That way you will have a reliable restore point to fall back to.

 

I've tried Colorful Disk Clean. YES, it's really a nifty and practical program. The most important thing is that it's quite cheap and simple to use. I personally think that it's much more powerful and useful than Disk Cleanup.

 

But, on what do you base that opinion? Have you measured the removed garbage on either?. Or by trying another third party cleaner? The results are pretty much the same. I, and I am sure many users, do not have any overwhelming desire to see a picture of the process.

I would not consider buying such a utility, with so many free options to do the same thing. But, as a matter of interest, could you explain how it can be compared with the built in disk cleaner or, for example, Ccleaner. It seems that it is necessary to select the files you wish to delete?

It is becoming typical of amateur Apps, in the store, that they are entirely unmonitored by Microsoft.. To present a program such as yours, which opens to a totally empty window, without any indication of help, is, imo, unacceptable