OK, so, I'm assuming teh image is in one of teh folders on your computer, and you're on a standard Windows platform...

right-click on the file you want to open/resize
Open with MS picture manager
Once it opens goto the word options at teh top of teh wiindow
select the word "picture"
go down to "resize" and select
It should open up some resizing options on the right of teh screen (or, perhaps in another window, depending on how it's setup
play with teh sizing options until you get something that fits what you need
(after you resize it it's a pretty gud idea to "save as" some derivitave of teh original name, so you can keep the original in it's original size/format)
When you quit out it should ask you if you want to save (the changes to teh original). If you've already done a "save as" then DON'T SAVE when given this option...

Any questions?