How do I increase my memory to 2 GB or more as I currently only have 1 GB?

Buy and install more RAM from a source such as OWC or Crucial.

(123352)

If you are referring to the iMac in your Tag line. i.e 2007. You'll need to buy more Ram. Your Mac should be able to take up to 6GB.

OWC Mac Sales

http://eshop.macsales.com/shop/apple/memory/iMac/Intel_Core_2_Duo

and Crucial

http://www.crucial.com/usa/en/compatible-upgrade-for/Apple/imac-%28mid-2007%29

are highly recommended.

Posting in a more specific area of the Apple support communities may also be helpful I'l ask your post be relocated there:

iMac

If you are going to add RAM DO NOT stop at 2GB. Add as much RAM as your Mac will hold. The cost between 2G and 6GB is not all that much.