Many Merc. outboards of different HP are identical except for carb jets, or control modules in the case of EFI motors. marine engine dot com, and other sites have factory parts catalogue pages. Open two browsers and compare your year's 135 and 175 parts. I searched your s/n and got :
Mercury / Mariner (135 / 150 / 175 / 200 / Xr6 / Magnum Iii) Engine Components
They show several carbs, so there is a good chance you can make yours a 175 or more HP with relatively inexpensive carb parts.
http://www.marineengine.com/parts/mercury_marine_parts/sn/0d166539
If you're successful, you'll need to pitch up your prop to benefit from the increase.
