That's a very old version of Reaper; here's how I'd do it in mine (5.983...), but it may be slightly different for you...
Under 'Options', right at the bottom of the drop-down list, I have 'Themes', which allow choosing between 'Default', 'Default_4.0', 'Default_6.0' and 'Classic_1.x'. One of those might help you.
Just beneath 'Themes', I also have 'Layouts', from which I can choose 'Default Layout' and a whole host of others, giving each different variants in the sizes of the elements on screen. Have a look there..?
Hope this helps, but it's not certain.