MC,
presuming you are using Windows above XP, open Paint and then open the photo you want to resize.
There should be an option to 'Resize'. Percentage should be selected as standard (if not select), ensure 'Maintain Aspect ratio' is checked and then enter a number below 100.
This will depend upon your original image size, so I can't help you there. However, if you select 50% and then 'Save As' and give it a new name (add Sm50 or somesuch, you can them hover over the saved file and see how big it is. Anything under 3Mb (3000kb) is good but I'd personally recommend under 1Mb (1000kb).
If the saved file is still too big, load the original file again and select a lower number and try again.