Upgrade the SSD in an iMac Retina 5K, 27-inch, Late 2015 from 250MB to a 2TB SSD

Yes, but specialized tools and parts are required. It is also moderately difficult and considered more of a technician-serviceable upgrade. See iFixit or OWC DIY install videos for more details.

A slower but much simpler alternative would be to use an external USB 3 SSD.

Hi OXFORDMAN,

I am assuming you mean 250GB, not MB.

You should not do an upgrade like this at home. Rather, buy an external SSD, and connect it via. USB.

Cheers,

Jack