Like the title.
How can i setup macbook Pro 13" earlier screen resolution 1440 x 900?
I tried from system references, the max resolution is 1280 x 800.
I use OSX Mountain Lion.
You can't actually increase the resolution of your display, as the panel is LCD and only has 1280x800 physical pixels.
You can however install and run Apple's Xcode from the App Store to allow your Mac to display resolutions (among many other things) found on other Macs to simulate the higher resolutions.
The display will be very pixelated and blurry though, as it's going to squash the visual elements from a larger virtual display onto a smaller physical display.
It has it's uses if you're a developer as you can design screen elements for larger displays and zoom to your native resolution in to see how they look, but I wouldn't recommend it for actual day to day use.