How do you change this basic word processing function...?

Whenever I type over an error on my daughter's cpu, it types over the words in front of it rather that moving the entire paragraph, so we have to hit enter to make the correction and then hit the backspace to put it back into its proper space. Is there a specific setting to change? This happens on her Yahoo mail, but not her Microsoft Office.How do you change this basic word processing function...?The symptoms should be the same in Yahoo mail and Office, but try hitting the %26lt;Insert%26gt; key again.