Complex sentence: With the need to update Russia's ageing fleet of Su-27 aircraft, Sukhoi in the early 2000s converted existing air force aircraft to include a glass cockpit and an improved weapons-control system to accommodate a larger variety of weapon.
Split into simpler sentences: With the need to update Russia's fleet of Su-27 aircraft, Sukhoi in the early 2000s carried out an upgrade of existing aircraft. To this end, the company in the first phase converted air force aircraft to include a glass cockpit, improved weapons-control system to accommodate a larger variety of weapon.