It depends on what you need to do. If you are just needing to make it smaller in width or height to post it, you can do that in the code to display it. For example:
This code: <img src="http://www.wdwinfo.com/sites/bbrazeal/JazzManOriginal.jpg"> will give you...
<img src="http://www.wdwinfo.com/sites/bbrazeal/JazzManOriginal.jpg">
But can be resized by adding either width="xxx" or height="xxx" like this:
This code: <img width="130" src="http://www.wdwinfo.com/sites/bbrazeal/JazzManOriginal.jpg"> will give you...
<img width="130" src="http://www.wdwinfo.com/sites/bbrazeal/JazzManOriginal.jpg">
You should use either width or height but not both. Use the one that is the largest dimension on the original clipart.
If you need to reduce the file size (measured in bytes or kbyte; find the size by pointing at the image and clicking the right mouse button; select Properties and it will tell you the Size: ) you will need to use some sort of image editing software. I mostly use Paint Shop Pro but an image can be reduced using Paint that comes with Windows. Go to Start, Programs, Accessories and select Paint. Open the file in Paint and under Image select Stretch/Skew. You can enter a percentage for both Horzontal and Vertical that are less than 100% to reduce the image and then save it.
If this isn't clear or you don't find Paint, etc. just post the image here and someone will reduce it for you.