I have about 400 pictures/videos on my iPhone, but it's taking up 6GB of space?

I have an iPhone 4S, and I believe that maybe one of the pictures is in HD? I'm only asking because I ran out of room on my iPhone, but my sister has almost 1000 pictures and just as much music as me. Is there anything I can do other than deleting all my pictures to make room for music?

Added (1). I've been deleting apps instead of videos and pictures. Is there any way to get longer videos onto the computer? I have a couple from a concert at my school but thats about it.

Videos take up A LOT more space than photos. Although the more HD the picture is the more space it will take, each one would only take up at most 2 MB. (400 x 2MB = 800 MB (0.8 GB. So you must have videos and probably apps that take up a lot of space, but you'll have to check that yourself.

You something must be in HD. You can take everything off you iPhone and then load it onto iCloud.

It depends are all your photos in your camera roll or old photos you've downloaded on to your computer and then reloaded on to your iPhone.

You need to get them on to your computer. So you can look at the details of each photo and see which ones are so large.

Check your videos too. Make sure you don't have any ten minute videos on there