The city has adequate public buses and you can also choose private taxis, if you don’t mind spending a few bucks more. You could book these taxis from the hotel itself and move around in style and total luxury and comfort.
It is a city that is bears proximity to Helsinki and hence, one can reach the capital city from Lahti, within one hour. Lahti is well known for its well developed public and private transport system. Hence, you should not have any problem moving around the city.