I use http://www.photobucket.com to upload my pictures. Once you've set up an account you can upload pics and then it's quite straight forward when you want to upload them to any forum.
You can use the photo gallery but I haven't used that yet! LOL! Have just looked and if you click on Gallery in the bar above you can upload your pics to there and then use the link to a post if you so wish.
Hi,
If you have Photo software you should be able to open the photo and resize it - keep aspect ratio and change the pixels size. Otherwise take your photos in a lower resolution on your camera - ie: approx: 2MP