Here is how you perform an Internet Recovery: You can then reinstall macOS via Internet Recovery, and restore the machine from the Time Machine backup afterwards (you will be asked if you want to restore from a Time Machine backup during the installation). I recommend that you create a Time Machine backup of your current HDD to some external drive before. The installation is incredibly easy to do, here is a video: Would I have to take it to an Apple store to replace the drive, or would it be easy enough for us to do ourselves? Two drives in the same machine is one of the most pointless things you can do with a personal computer.

While technically possible to replace the DVD drive, I wouldn't do it, as you can replace the HDD already. Most people prefer one drive only, because that's easier to manage. I mean, why would you do that, seeing how you can replace the HDD with an SSD already? What's the point? To have two drives in the same machine? That's actually annoying because you never know on which drive some files you have just saved are. I don't know why another commenter has recommended that you should swap out the internal DVD drive for an SSD. Here are some very well rated SSD models that should work flawlessly in your machine: Any internal 2.5' SATA SSD I know of can take an extreme number of write cycles, and every 2.5' SATA SSD I know of is likely to outlive the MacBook Pro 2012 machine itself, meaning some other component of the machine itself will likely break down before the SSD does. Honestly, it doesn't really matter which SSD you choose. This comment explains the difference well: The Samsung 560 PRO for example can take double the write cycles of the Samsung 560 EVO. The only real difference between them is durability. They all reach about 550 MB/s read speeds and about 520 MB/s write speeds. One thing you should know is that there are almost no speed differences between internal 2.5' SATA SSDs anymore. Any SSD that matches the following criteria.

External dvd drive for macbook pro 2012