There are many different ways of resizing photos.
I would suggest using Photofiltre, a free photo editing program you can download
HERE.
Download and install the program. I've suggested this program because of its simplicity of use, and the fact that its free. You'll find yourself doing many editing tasks with this program in no time, including colour and light correction, cropping and resizing etc.
Open the program ( Photofiltre ) and click on File>Open. Navigate to the photo you want to edit, and select.
Now right click on the photo, and choose 'image size'. Change the top field (width) to 650, and the bottom field will adjust itself to keep proportions correct. Click on OK.
Now right click on the photo again, and choose 'Save as'. Choose a name for your new edited photo, choose a save location ( keeping the other default save settings when they come up ) and presto.. your file has been saved in a web friendly size in the name you chose for it.
Now all you have to do is upload the new slim and trim photo.