Mismatch between video and audio time line in avi video

I have a video tutorial created for educational purpose and is about 380 MB. The problem here is that the audio lag video by approximately 6 seconds. Can I repair this video? Will it help if i convert this video to other format? For my programming purpose the video has to be in avi format only. Are there any easy to use tools or software which can correct the difference between audio and video timelines? Why does this lag basically happen? Will it repeat even after correction? Is there a way to detect the time difference accurately between audio and video?
