Converting video files HELP!

My problem is I want to find some software or a program that lets me convert videos to a bigger picture size. Like from mp4 size to like a decent avi size like 640 X 480. Any help would be great.
Answer #1
up sizing any image, movies included, will introduce artifacts, mostly blockyness
if you convert them, stay at the size they are at an let the player resize them
give TMPGEnc 4 Xpress a try
search “Xpress” in appz section
you can also check this out
http://www.videohelp.com/tools?convert=MP4%20to%20AVI