adobe reader upgrade

i just download adobe reader 8 and i still have acrobat reader 6 in my computer, do i need both or can i delete the older version?

You really don't need both versions of Acrobat Reader since version 8 will open all older PDF documents as well.
I have found that if I un-install the older version, this often causes the newer version to stop functioning as well. The best thing to do, is un-install the older version before installing the newer one.
Since you both have already installed, I would suggest you go to the Control Panel and using the "Add/Remove Programs" applet, remove both versions of Acrobat Reader.
Once you have re-booted your computer, you can re-install Version 8.