Question about Apple iMac Retina

However, it is possible with a great deal of effort, not to mention that all warranty claims are gone when the unit is opened! The retina screen is glued to the case. There are various instructions on Youtube. The tenor of these instructions is that it is very time-consuming! Apple will release a new iMac in the near future. Better wait and order the device with an SSD.

It is possible, but you have to dismantle the screen, which is glued.
It is a difficult and complicated procedure. There are instructions on the ifixit website, but they are not recommended for beginners.