Ask your local library if they could use any of your computer books. Inquire about any policies pertaining to the age and condition of the books. Larger library branches generally will want computer books on specific topics while smaller branches generally want books that are more broad in nature.
Donate your old computer books to a thrift store. They are usually less picky about book dates and conditions than libraries. Many thrift stores give part of their earnings to charities, so be sure to donate to a cause that you stand behind.
Give your old computer books to any family members, friends or neighbors that could use them. There are many people in your direct community that could benefit from this, so reach out to see who may be interested.
List your books online using a free advertising source. This is another way to get your books into the hands of someone who needs them.
Donate the old computer books to homeless shelters. There are many poverty-stricken people that could greatly benefit from learning computer skills.