Today, I got a bigger SSD because mine used to out of space all the time. I already opened my MacBook Pro (2011) quite some times but I never actually changed the harddrive. Therefore I checked some blog posts about how to do it and it was as easy as from what I remember from doing it with my Thinkpad, maybe even easier
So I plugged it in the USB port with the nice little adapter Samsung ships it with and partitioned it with the Disk Utility which comes with your Mac OS. Afterwards I downloaded the Carbon Copy Cloner, which has a free and fully functioning 30 day trial period, started it and used it to clone my former harddriver. Finally, I installed the new one in the adequate place and that’s it.
Everything worked right away => perfect
Please note that you will loose the recovery partition when doing this, so you won’t be able to use FileVault2 nor the “Find your Mac” iCloud feature!
To regain these features you have to download (AppStore) and reinstall Lion (+ all the updates afterwards).