ATC Scm 19 V1 Upgrade or what?

Assume you have money, so I unabashedly recommend the ATC 19A or even the 40A which will smoke your current setup.  And not that your current setup is wanting.  Active will get you there.  Period.

The V2 SCM19 sound significantly better than the V1. There was a tweeter change to the 19V1 plus some crossover changes that make the speaker sound like it is "more" than just a tweeter part change.

The 40 is ATC’s most popular consumer speaker because it is the lowest cost way to get the mid dome. I think 40s are the bargain of the audio world, active or passive. Will punch above its weight in both forms.

The other upgrade is the 50s towers, with the mid dome and the same SL technology in the 9inch woofer as the 19’s 7 inch. Ultra clear bottom to top.

20s are different than 19s, set up brighter for mixing. I prefer the 19s for home use as they sound subjectively warmer. 20s work out well in studios that need a nearfield, studios that are often very absorptive and the engineer wants the recording flaws pointed out first and foremost.

Brad

An additional thought. While some might prefer the extra detail in the 19s, many would agree that the 40s represent an overall improvement to the sound, depending, of course, on the room and all the other variables. This strikes me as a valid point of view, even if I disagreed with it.
To be fair, I may be overreacting to past posting trauma when others were unkind to me after I asked stupid questions (and they were).

From the OP's post, I assume he means a wholistic or general improvement to SQ (to his ears). Sure, some of us could better help him if he had something specific in mind, but I know my orientation/understanding doesn't always afford that when I ask a question on here. (Which makes me equally annoying to some, I'm sure).
Anyway, if we can offer help on the OP's terms, however limited that may be, it's still help. 
Of course, it's also a form of help to let the OP know that specifics are really useful in question asking, especially about what would improve a system.

op

no commentary on what you are trying to improve in the upgrade?

if the mere objective is to buy the more expensive bigger model then that mission is most easily accomplished...

anyhow, there are many paths to hifi happiness, wish you best on yours

The SCM40 will work fine in your room assuming have the time, patience and skills to properly set up speakers and listening position.

Jim Smith's Get Better Sound book is a great guide.

My room is nearly 5x3 m .. I'm not sure if it's big enough for scm 40 

I agree with VV. I think your best bet is to go to the passive SCM 40 V2 with the ATC amp you already have. It will be just fine driving the bigger speaker.

what are you trying to improve?  not specifying will just lead to nonsense replies

I would move up to the passive 40, a big improvement over the 19 (either version).

Yes, plenty of power, a great match.

The pro active 20 is roughly the same price as the passive 40. Since you already have ATC amplification, the 40 will give you more bass and plays louder. You don't have to deal with stands. Yes, going active with ATC will give you an improvement over passive but I'd still go with the passive 40s in your case.

Besides, the pro SCM20ASL is backordered at least a month, probably more; extremely high demand. You won't find it anywhere discounted below $6490 and good luck finding a used pair.