LIBREVILLE, Jan 10 (Reuters) - Air Gabon said on Thursday that it planned to replace four old aircraft with new planes -- a Boeing (BA) 747-400C, a Boeing 767-300ER, a Boeing 737-800 and a Boeing 737-700. The central African state's flag carrier leased two Boeing-737s recently to increase its fleet to six aircraft and allow it to raise the number of flights within Africa as well as to Europe and to Dubai. Air Gabon has been going through a slow restructuring since 1996 as a prelude to privatisation. It is held 80 percent by the Gabonese state and 20 percent by a company jointly owned by Air France and a French state financial institution, the Caisse des Depots et Consignations.