[…] the installation of four 14,900 lb st (66.3 kN) BMW Rolls-Royce BR710 turbofans in place of the Speys, the fitting of a new two-man cockpit and a modern tactical operations area, and 'zero lifing' all existing structure and equipment.
Source: wiktionary
The first element involves 'zero lifing' the airframe by replacement of some structural elements, including the main landing gear. This "extends the operational life before the first major overhaul and extends the time between repair", Filip said.
Source: wiktionary