Up and down shifting is all based on the load you're placing on the engine. There is no magic RPM that we can tell you to shift up/down at aside from staying out of redline. If you're uncertain leave it in D then experiment in a safe environment.
I don't know where the OP lives or what engine they have due to their blank profile but in the US we don't get that feature.I believe it will advise you on the display. It certainly did on my diesel auto.
That looks like an excellent feature for someone that is learning to drive stick, but should have the option of turning off.Man, I am glad we don't have it! My ex-wife had a Ford Escort GT back in the day (for a small car, that thing drove like a tank) and the little yellow "shift now" light would come on at certain RPMs. It just about drove me crazy. Yes, I am a grown man; yes, I know when to shift and I will do so whenever the heck I want! I wish I could disable my wife's Fit's "economy" lights (one on either side of the gauges). They glow green when one is being "economical" and when one is ruining the environment, dark blue (it should be red with images of rising sea levels, melting glaciers and a lone polar bear on a piece of ice...)