If you don't have night sights already installed, you can take it to a good gunsmith for them to machine the front dovetail and install the aftermarket sights
If you have the old model like I do(with factory night sights), you have to send it back to factory or to Night Sight company(Trijicon, Meprolight or who ever) for them to punch out the old tritium vial(s) to replace it.
I want a new style Beretta with dovetail cuts already milled in the slide with front cocking serrations on the slide and would love to have it in calibers like 9x21, 38 Super or 9x23!!!!!!!!