If you have to ask then the full answer's pretty much certain to be beyond you.
Alone, the isolation of psilocybin presents a significant practical challenge. The reductive lopping-off of a phosphate group which is both labile and acidic presents even greater technical challenges - and psilocin, the unphosphorylated mushroom alkaloid, is notoriously fragile. You aren't going to be able to do this in your kitchen, basement or garage. If still you want to have a try you'd best prepare to study for a chemistry degree.
Why the heck would you want to turn psilocybin into DMT anyhow? It's basically orally active DMT that doesn't require MAOI. I can only presume you'd prefer something with a shorter duration.
There are easier ways of obtaining DMT. Welcome to the Nexus!
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli