Photoshop is expensive and not worth the price if these basic things are all you are doing.
GIMP is the free solution which allows for almost the same things as Photoshop.
GIMP is a mighty tool. Lots of options. One needs to get used to it, but there are a lot of turorials on the net. It's available for all platforms, including Windows.
And here is a HowTo for GIMP and resizing images: