May available for the Leon, don't know too much about the diesel versions to be honest.
I think lots of people have trouble with DPF on the diesels but don't quote me on that. I tend to steer clear of topics that don't affect my engine or ones I have knoweldge over.
Still having said that, you want a re-map which can be obtained amongst others from Revo or Custom Code etc.
Essential this is a reprogram of the engine management through the port and results in more bhp/torque and often better economy too,
for the 2.0 TDI you should expect to see bhp increase from 170 to 208, torque 258 to 321 or numbers close to that.
See revotechnik.com and look up your vehicle, find you local dealer, probably around 400 notes b4 VAT