Question How do i make my sig pic 500x200 using photobucket

You don't, the image must be 500x200 in the first place. this is done by using a photo editor such as MS Paint or Adobe Photoshop...

 

Actually, you can resize it using Photobucket.
Upload it, click Edit, and resize it.
You can resize it proportionally, or not, just check/uncheck the box.

 

I stand corrected...

 

In Paint, go to Image and click "Attributes". Then just type 500 in the "height" box and 200 in the "width" box. Although I don't recommend using Paint for sigs, I don't know how to use any better programs