If you are using paint it is possible to resize. Firstly use the select tool to draw an elastic band around your pic. Drag this so it is in the top left hand side of the work area. Click elsewhere outside the box to finish this, the elastic band should disappear. If you look to the bottom right hand side of the white work area there should be a small shaded box. Click on this box and drag it to alter the size of the work area.