How can I make a Jpeg file smaller for emailing purposes?

I need to send scanned doents to someone thru email and they can only accept attachments upto 12mb but most of my files are 20+mb. I need to make these scans smaller to fit the email but i also need it to be legible n printable for the person receiving it. How can i do this? The files are stored on corel and picasa. HELP!