First, if you're flying with Scoot Airline and Cebu Pacific most likely you'll be landing in Terminal 2 (Changi have 3 terminals so far). Once you have landed exit will bring you directly to shops/boutique, money exchange and such in second floor (Note that second floor is for arrival, 1st floor is for departure). Then to exit the airport you need to take escalator/elevator to the ground floor for the immigration. Before proceeding to immigration take some time to walk around the 2nd floor and take some photos and exchange your currencies. Walking straight up to the left will bring you to departure gates make sure not to exit in the left wing, better yet do not take the escalator going down from the left wing.
Here's what to expect around 2nd floor.
