PARIS (Reuters) - Air France-KLM (>> Air France-KLM) said on Monday it is overhauling its Flying Blue frequent-flyer programme, hoping to increase its contribution to sales.

The Franco-Dutch airline group said it had spent two years and 15 million euros (£13.2 million) on IT to overhaul Flying Blue, the joint loyalty programme of Air France and KLM with 15 million active members.

From next April members will earn miles based on the amount they spend on their ticket rather than the distance flown, with status members receiving more miles per euro spent.

Status levels will also no longer be earned by racking up a specific number of flights. Members will instead collect more points for longer flights and for those in premium cabins.

The two airlines earn nearly 55 percent of their revenue from loyalty schemes including corporate contracts with companies and the Flying Blue programme.

Air France-KLM CEO Jean-Marc Janaillac said the group wanted to increase by 10 to 15 percent the proportion of sales that Flying Blue contributes to turnover at the airlines.

"It is a profit centre," Frederic Kahane, head of loyalty at Air France-KLM said.

Airlines tend not to give details of the profits they make from their loyalty schemes, but several have tried various strategies to release cash from them.

Air Berlin (>> Air Berlin Plc), which ended operations last month, sold a 70 percent stake in its loyalty programme to major shareholder Etihad in 2012 for more than the market value of the German company as a whole at the time. In 2013, an IPO of Smiles helped Brazil's Gol (>> Gol Linhas Aereas Inteligentes SA) bring down its net debt.

Air Canada (>> Air Canada) separated its frequent flyer programme Aeroplan in 2002 but said in May it wanted to launch its own loyalty programme, hitting shares of Aeroplan's operator Aimia (>> Aimia Inc).

Air Canada said bringing the programme back in-house could be worth $2 billion-$2.5 billion (£1.5 billion - £1.9 billion) on a pre-tax basis over 15 years.

More recently, airlines such as British Airways (>> International Consolidated Airlines Group) and Delta (>> Delta Air Lines, Inc.) have tweaked schemes to mean the amount of miles earned is based on ticket prices, such that premium cabin flyers earn more miles for the same journey than those in economy.

(Reporting by Cyril Altmeyer; Additional reporting by Victoria Bryan in Berlin; Editing by Hugh Lawson)