To find out which firmware revision your SSD is running, follow these steps in OSX:
Click on the Apple menu
Select "About This Mac" (then "More Info..." if present in your OS version)
Select "System Report..."
In the Contents list, click on "Hardware" to expand the category
Click on Serial-ATA (near the end of the Hardware category)
The drive attributes will be displayed on the pane on the right. You will see the name of the drive i.e. Crucial CTXXXXXXX, the drive capacity etc. The firmware version will show in the 'Revision' field.
If you want to know how to find this information on a Windows PC, go to this article.
If you want to know how to update the firmware to the latest revision, we have posted a guide here.