you probably have everything you need right there.
go to the pic you want to resize
right click on pick & choose "open with"
click paint your pic should come up on screen very big
at the top left of window will be image click that
click "stretch, skew new grey window will appear with Horizontal & under that vertical with numbers in boxes
in the boxes change numbers to 50 on both & click ok.
You can do it again if it is still too big.
then save as - - - I usually tag mine with 'email so I know I can send it.
number varies of course, you can put in 25 or 75 but I do 50 & go from there. let me know if it works.