OP:
If by your original post you mean that you intend to swap out the HDD for the SSD, I would like to offer some advice.
My strongest suggestion:
"Prep and test" the new SSD -externally-, BEFORE you "do the drive swap".
This way, if you encounter any problems, you will still have a working computer with which to solve them.
You will need an external USB3 enclosure, but this will come in handy anyway for the old HDD.
I suggest when shopping for an enclosure, that you ONLY buy one that SPECIFICALLY STATES that it has "UASP support". This is needed to achieve the fastest speeds that USB3 can offer.
Numerous enclosures are available at places like amazon for $20+/-.
Put the SSD into the enclosure
Initialize with Disk Utility.
At this point, you have to decide whether you wish to do a "clean install" or if you'll be happy by just cloning the contents of the HDD to the SSD.
If you're going to clone, either CarbonCopyCloner or SuperDuper can do the job.
I would suggest CCC because it also clones the recovery partition if you wish.
Once the OS is installed, do a test boot.
Restart and hold down the option key until the startup manager appears, then select the external SSD and hit return.
Do you get a good boot?
Does everything look as you want it to look?
If so, now is the time to power down and do the drive swap.
One important advisory:
Be sure you use THE RIGHT TOOLS for the job.
I think you'll need a Phillips #00 screwdriver and a TORX T-6 driver.
Available at hardware stores, Home Depot, Lowe's, online, etc.
Once you get the MacBook buttoned up, restart and again use the option key trick to invoke the startup manager. Select the SSD (now internal) and hit return.
Again -- do you get a good boot?
If so, be sure to go to the startup disk preference pane and designate the SSD to be your boot drive.
Also, as Weaselboy said above, you can use the terminal to turn on TRIM...