how to do my transmittion gear..

I have safari td 42 diesel/2000crazy this brand at least 7years
now my car not to change gear over 60 kmh ..help me please

Have you changed the transmission fluid?
Do that first

I'm assuming its auto, so will reply as if it is

Could be many things wrong.

Worn clutch plates

Stuck solenoid

Has it ever been serviced other than just an oil change?