Instead, you need to plan your upgrades at the time of purchase. In other words: no more post-purchase upgrades. The late 2014 update adds dual Thunderbolt ports and faster 802.11ac Wi-Fi (as found on the rest of the current Mac line), but the RAM, which was previously user-accessible, is now permanently soldered to the motherboard.
But if you go back to the last major Mac Mini update from 2012, you'll find quad-core Core i7 chips, a more powerful option now missing.
Two more-expensive base configurations include faster Core i5 CPUs, with a dual-core Core i7 as a extra-cost add-on on top of that. The processor in the $499 model (£399 in the UK and AU$619 in Australia) is a dual-core, low-voltage fourth-generation Intel Core i5. But, underneath the matte aluminum chassis, there are a few areas where the current iteration of the Mac Mini may not work for you.