An easy way to boost performance if your 2014 Mac mini still has a hard drive. 

Includes what you see in main photo:
The screen shot shows details of drive, taken before carefully removing from mini.

The final photo is to illustrate what it would look like installed.

Note that the cable was held on with adhesive, as well as the mounting screws. There may be enough left to re-stick, but you may want to also use tape or additional adhesive if unsure.