Now that your original hard drive has been successfully cloned to the new SSD, you're ready to install the SSD in your MacBook. First, remove the SSD from the external drive enclosure. After fully shutting down your MacBook, flip it upside-down. The rest of this guide was made with an early 2011 MacBook Pro 13" in mind, but the process for other MacBooks should be similar. For model specific guides on how to replace your Macbook hard drives, you should check out OWC's Tech Center or iFixit for guides.
Use the Phillips 00 screwdriver to remove all of the screws on the bottom. The bottom panel should easily be removeable after all of the screws have been taken out.
A small black plastic bracket that secures the hard drive needs to be removed. Remove the two screws as indicated in the photo below.
After the screws are loosened, you should be able to easily lift the bracket up and off.
Carefully pull out the hard drive, keeping in mind the ribbon cable is relatively fragile. Hold the connector firmly while pulling it off of the hard drive.
There are four Torx T6 screws which need to be removed from the hard drive. There are two on each side of the drive.
Re-install the four screws on the SSD.
Now reverse the steps taken in removing the original hard drive, but with the SSD. Reattach the SATA data/power connector, slide the SSD in place, and secure the mounting bracket.
Confirm that the newly installed SSD is secure, then you can replace the back aluminum plate onto your MacBook.