vauxhall astra gears?

xreg 2000 model vauxhall astra 1.6 having trouble changing gears?

i have vauxhall astra 1.6 having problem changing gears in the middle of the traffic and fine to start with but after a while when at round abouts and right turns trouble to cgange gears please suggest solutions the car has done only 30k miles and otherwise good car please help how to solve this