Thank you for the reply.
You may try to install the Z540 or higher. However, Dell doesn't recommend a processor upgrade as it is very complicated, and a higher processor will generate more heat and may create compatibility issues.
Internal hardware upgrades are suitable for desktop system, where you have ample space to accommodate the new hardware, upgrading internal hardware in a mini system would be a risk.
If you are looking for a compact and powerful system, you can check out the Dell XPS 10 and 12 systems.
Please reply for further questions.
Thanks and regards