You can open it in just about any photo editing program and resize it. A good resolution in somewhere between 600 and 800 pixels wide. A picture of that size is detailed enough and will easily be under 80kb.
Photoshop is a great program, but a little much just for resizing. If I'm just resizing, I use simple programs that open and do their job quickly. I use ACDSEE, you can find it free at download.com
Here's a link.
http://www.download.com/ACDSee-Standard/3000-2204-10324094.html