It's one of those if you need to ask, you can't do type of operation.
If you insist, here is the general breakdown:
* Remove the screen assembly from the phone and remove critcial parts like the home button, ALS/top speaker flex and so on.
* Cut open the plastic screen frame and pull it off the glass.
* Use thin molybdenum wire to cut through the LCD optical bonding to the panel so you can separate the panel from the glass.
* Use solvents to wash the remaining optical bonding from the LCD panel.
* Apply new optical bonding adhesive to the LCD panel.
* Attach the LCD to the new glass panel, align it properly and avoid trapping any debris between the bonding.
* Use a vaccum lamination machine to properly bond the optical bonding layer to remove any air bubbles.
* Adhere a new set of screen frame onto the glass.
* Reassemble critical parts and the whole phone.