Find the picture you want to resize and right click on the icon.
A drop down menu will appear, click Edit.
This will open the picture in Mspaint.
In the upper left hand of the screen click on 'Image', then click 'Stretch and Skew'.
There are two field in the Stretch part of the box, a horizontal and a vertical. These will shrink or expand your pic as you want.
I usually punch in 40 in both fields and it resizes them appropriately but you can punch in any number you want. Any set of numbers less than 100 will shrink the photo and any numbers greater than 100 will expand the photo. You also want to make sure you type equal numbers into both fields or it will stretch the photo irregularly, ex. 35 horizontal and 35 vertical or 60 horizontal and 60 vertical.
Also, if you ever want to see the size of a photo you simply right click it and select properties, if the pic is greater 1Mb then it's pretty big. I try to shrink mine down to around 300kB or so. And never save a photo as a Bitmap, they are HUGE files, always choose a Jpeg when you have the option.