I'd say that you should get your tracking checked (unless the garage did it already) since you have lowered the car, then you'll know that the steering is working at its best and you can get a feeling for the tyres you've got on now. You can check the tyre pressures are correct too as Ziggy said.
Then just use up the tyres as they are... if you're doing a fair mileage you should get through them OK unless they are rock hard, in which case you'll soon lose confidence as the weather gets worse. Obviously the fronts will be the ones to wear out, the rears are important but they don't do much work.
Ideally you would wear out the older tyres first, there are codes on the sidewall that give the week and year of manufacture (e.g. 32 11 = week 32 of 2011).
See how you get on then make a decision.