Driving up a slope is just the same as driving on any other road. On a flat road you wouldnt shift into a higher gear if you didnt have enough momentum, would you? Similarly, on a incline, you cannot do he same. If you have stopped on an incline, you need 1st gear, period. If you have just started moving, shifting into 2nd will make the engine struggle a bit as it is loaded with less fuel (i.e. less revs). On an incline, you need to overspeed in a lower gear before you shift into a higher one- go to 20 or so before you shift into 2nd, for example, because by the time the gear engages completely, both the engine (in terms of rpm) and the car will have lost come of its momentum and you will feel a jerk. Nothing surprising about it, thats just getting used to driving on steep slopes that we dont do regularly.
For the record, my Swift (which is same as the Ritz mechanically) can go up bridges here in Mumbai even if 5th gear if I am doing 50+. At below that speed 4th is required.
I would just say learn to listen to what the car is telling you. If you do, you will hear it asking for a certain gear at a certain time. If you prefer to use the tachometer, keep it in the 1500 rpm range atleast before you change gear
Ameyam