New to Making Video on iPhone 5s

My first attempt at making a video with my iPhone seemed to work ok, but after downloading to the computer I noticed the video is sideways. I was told later to keep the phone vertical when videoing. However is there some program that I can use so I can flip the video so that I can post it online and it comes out straight and not sideways? I found a free program that flipped the video so it plays with VLC and WMP but the video still posts online sideways?

 

the phone can be held vertically or sideways when recording, the orientation is decided when you press the record button so if the phone is vertical when the record button is pressed then it will stay in portrait mode and vice verse when the record button is pressed when the phone is horizontal.

so i am assuming you pressed the record button when it was in vertical mode and then held the phone sideways.

i have used a program called Sony Vegas to change the orientation of videos but it quite expensive, maybe you could try the free trial or someone could chime in with a cheaper/free alternative