Daihatsu terios 2010, 7 seats, A/T, overdrive

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Hi,
I have Daihatsu terios 2010, 7 seats, automatic transmission car, the transmission has only 4 speeds automatic, which is bad for high speeds,
I read that 4 speed automatic transmission can be converted easy to 6 speed transmission,
did anyone tried this with this car???? and how to do this???

Best regards.