How do i change the size of pictures on my computer?

every time i save a picture it saves as the 320x240 size. well i think thats what it is, and it wont save a bigger size when i download it from an email. i dont know how to change it. please help?How do i change the size of pictures on my computer?
Right click on the picture.



Choose the ';Open With'; option.



Choose ';Microsoft Windows Picture Manager';



At the top bar, choose the Picture option.



Choose ';Resize';



It's pretty self-explanatory from there.

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