IaaS is just like leasing a Car/Bike; you can drive the car/bike to whichever place you want, but the car/bike is not yours. You have to return back after usage. If you need some up-gradation, then you might go for some other car/bike.
PaaS is like taking a taxi or cab; here, we (means the users) don’t drive the cab himself; instead, there is a dedicated driver to do it; we just have to tell our destination and relax. The driver does everything