Then click on Image>Resize. You should see a pop-up window in front of you looking like this:
Change the width and height to a number of your choice.
At the bottom of the window before the OK button there will be options looking like this:
Smart size means it will resize it normally. so if your image is 100x100 and you wish it to be 90x75. It won't resize that way. In other words it'll resize your image to make it look even. When you're done everything, click OK.
My result:
