Well, if it's just a little stretch, you might only have to make subtle changes to the uv's. If it's a major stretch, I would consider laying out the uv's. If you choose EditPolygons>Texture> you'll see several mapping commands. You can map several faces at a time or the whole thing. It really depends on what the geometry on your model looks like. I would suggest going through several uv mapping tutorials to get the basics down as uv's are a bit confusing at first. You have the type of mapping, your uv shells, specific ways to move shells, you can sew uv edges together, etc, etc.
Alias|Wavefront has a uv texture DVD out. It's extremely boring and the resolution is absolutely horrible, but it deffinetly teaches you a lot about uv's.