New to Applescript - Need script to delete unwanted text

I have a large text file and need to delete certain names from the file. For example, one item has 20 descriptions for it and I only need it to have 3. The file is large and need it to be automated as easily as possible. Can anyone help?

Browser: Internet Explorer 5.23
Operating System: Mac OS X (10.3.9)

I think we need an instance.