Kolpino is full of marshrutka-minibuses and larger ones. Most of them are on the routes Kolpino-Zvyozdnaya metro station (south of St. Petersburg) or Rybatskoe metro station (south-east). Final stops are clearly marked on the wind screen and side window. Expect to pay arount 10 to 30 rubles depending on the length of your trip.
There also is a railway station in Kolpino, at which the electrichkas on the main line (SPB-Novgorod, SPB-Malaya Vishera etc.) stop at. Trains leave from Moskovskyi or Obuhovo. More information on trains http://www.tutu.ru