Not sure what you mean by "space" so I can suggest 2 ways for you. (Please do not use the 1st way if you don't understand what you're doing, otherwise you might shut down an important process on your computer.)

I assume you use Windows as your operating system.

1. Press the buttons Ctrl,Alt,Del together. If you use Windows XP or below, then a program called "Windows Task Manager" will automatically pop up. If you use vista, you might be asked to choose from a list of options -- please select "Start Task Manager" and then the program will pop up.

Next, click the Processes tab. You will see a list of all the programs and processes which are currently OPEN on your computer. (For example, if Microsoft Word is installed but currently not being used, then it will not show on the list.)

Click Mem Usage twice. Now the programs are organized by which one takes up the most memory. From there, you can make a list of which big memory-eating programs you don't want anymore. Then you can go to the 2nd method below.
(Or, if you need to shut down a certain program immediately, select it from the list and click "end process" -- do this at your own risk! be careful.)

2. Start > Control Panel > Add or Remove Programs
This will show you a list of programs installed on your computer -- on the right side of the box, it shows the "size" of each program. You can uninstall any unnecessary programs if you feel they are too big.

Hope that helps.