We have a file limit so you wont be able to upload larger files you have without resizing them. You can even upload your own drawings by scanning them, converting the bitmaps to jpgs and resizing them.
First Download Ifranview. It's a small 1mb program for editing images. Select no when asked if you want to install google desktop search during the installation process.
Select Image -> Resize/Resample. Change the width and weight. Uncheck preserve aspect ratio if you don't mind having the ratio of height to width changed.
Click File -> Save As. Select JPG. Mess with the quality and size of the image until you get the results you want. Irfanview has many other cool features you can use on your images so play with it.