To reduce the size of an image, you need to use image editing software. You may have software that came with your camera, or you may have Microsoft Photo Editor, which comes as part of Microsoft Office or Microsoft Word. Click the Start button and look under All Programs to see if you have image editing software.
There are also online photo editors. Picnik.com is free for the basic version, and will let you edit your photos without registering and without sharing them online.
In Microsoft Photo Editor, or other image editing software, open the image you want to use on the site. Immediately Save As and give it a different name. Never work on your only copy of an image, always make a second copy and work on that copy.
If you want to, crop the image to place the main subject in the centre of the picture and get rid of unwanted clutter around the main subject.
In most software, the command to change the size of an image is Image - Resize. Set the size to the necessary width (perhaps 240 pixels) and the height should adjust automatically. If you have the option, set the resolution to 72 dpi (dots per inch). You may want to experiment with some of the effects available. (Now you know why you should not work on the original image, but only on a copy.)
Click the image button (the one with the mountain). In the dialogue box, click the Browse Server button. At the bottom of this dialogue box, click the Browse button. Navigate to the folder where your picture is, and select it. (In the file selection box, you can choose Thumbnails from the Views button if you need to see the images.) Click the Open button.
Click the Upload button. When the upload finishes, the image will appear in the the list of available images. Click the image and the dialogue will close. You will see the image in the final dialogue box. Click OK.
To place a caption under the image, click the image, then use the right arrow key to move to the space immediately beside the image. Press Shift-Enter to move down one line and type your caption. You may need to centre the image and/or the caption.