I've downloaded it onto my laptop but is there now a way of rotating it?

Best in computing forum really.
Need a bit more info eg what pc, what software etc

Anyway, if you have windows, then movie maker is standard, try this link:
http://answers.microsoft.com/en-us/w...3-18c1bb243bd6

Which way are you holding the phone while your shooting the video?

Normal like when your making a call or sideways like holding a camera?

Stiggles has asked the right question here. I bet the OP has been shooting video whilst holding the phone in portrait mode. Easily done when using a phone.

Holding the phone in the correct orientation will only affect future videos but not the one already made.

Seems pretty daft that you can't take video in portrait mode, the phone should auto rotate the video to however your holding it.

It's exactly the same when you use a digital camera to take video. You can't do it in portrait mode. Well, you can, but it won't display correctly on a computer or TV.

If you hold the phone vertically, the footage is portrait. If you hold it horizontal, the footage is landscape. If you rotate the phone, the footage rotates.
Assume the OP has a mixture of portrait and landscape or has portrait when they want landscape. The link in #2 is a starting point to resolving it.