Download El Capitan installation from the App store. It might complain that you already have it installed but download it anyway. It will be downloaded to /Applications and be named Install OS X El Capitan.app
Create a bootable image from the El Capitan installer on a USB stick larger than 6GB. In a terminal run:

where MyVolume is the name of your USB stick. Change this to match the name of your USB stick.

Install El Capitan Dmg

Quit Disk Utility and install El Capitan. If you already attached the SSD you can use Internet Recovery Mode (hold cmd R or alt cmd R while booting) to first partition the new internal drive and then restore the original system (10.7 Lion). Then - after configuring Lion - you can to upgrade to El Capitan. MacOS – OS X internet recovery older version problem. I am using Macbook Pro Mid 2012 13' with 128GB SSD. The latest installed version of OS X was El Capitan which crashed during a Sierra upgrade. Internet recovery mode worked somehow to land me to install download and install a new OS but it's Mountain Lion, which came installed when I. My thinking is: 1.take out the old drive. Insert new memory + SSD, re-format, 3.load Snow Leopard from my CDs (I got them when I bought MBP back in 2011), 4. Download from Apple and upgrade to El Capitan.5. Only now migrate old data from HDD to SSD (for HDD I have an external hard drive enclosure ready).

Physically install SSD into the target laptop.
Insert the El Capitan USB stick into the target laptop and power up. (This might take a while.)
When the menu finally turns up, choose Disk Utility and format the SSD as Mac OS Extended (Journaled) with a unique name.
Once complete, exit from Disk Utility and return the main menu.
Choose to Install OS X on the formatted SSD.
Follow the prompts until El Capitan is installed.

Here’s link to a video on how to physically install the SSD as well as run the software installation.

Install El Capitan On External Ssd

If you’d rather install Yosemite on the SSD then follow the How to Install Yosemite on a New SSD guide.

Install El Capitan On New Ssd