It's actually good that they're huge - you can always reduce images, but you can't blow them up without ruining the quality. There are a lot of different ways that you can resize the images. The software that you use to upload the images might have the ability to do this. Adobe Photoshop is great, if you have that. In Photoshop, you just select "Image -> Image Size" and type in the size you want. If the "Constrain Proportions" box is checked (and it should be by default), then it will preserve the image's original proportions. You might also want to crop the image. If you don't have Photoshop, GIMP is also good and free (see
http://www.gimp.org).