The rear sight base on a K98 military Mauser is soft-soldered in place. The single set screw is loosened (while heating the rear sight with a propane torch) and the sight simply tapped off with a brass punch and hammer.
When replacement sights are installed, the sight base is fluxed, heated with a torch, the rear sight aligned, and the set screw set to hold the sight base in proper alignment while the solder hardens.
The front sight hood should simply slide on and off. Try rapping it with something soft, like a block of wood.