You just need to pass width and height as extra parameters to
tep_image()
function, the function already support them. From documentation:
tep_image($src, $alt = '', $width = '', $height = '', $parameters = '') X-Ref
The HTML image wrapper function
So it will look like
echo tep_image(DIR_WS_IMAGES . "arText.png", "ALTERNATE TEXT HERE", "width_here", "height_here");