Slitherine

Could I upgrade unit's size in CoW as in Legion? If yes, how I can do this?

Thanks

You cannot upgrade the size of units already produced, but building larger barracks will produce larger units. The ability to upgrade units was one of those little details which was dropped between Legion and CoW, and was not used in Spartan either. I miss that feature, along with the construction of military units taking an excess population unit. They reinstated that requirement only for peasant units in Spartan, so you could transfer population between cities.

I make it a priority to produce Barracks level 3 as soon as I can reasonably afford it. By the time I can produce Swordsmen and better auxilia, I already have a barracks capable of building the larger squads. Since you can only field 8 squads in a stack, it makes sense to field larger units, although I find that the "cost-to-benefit ratio" seems to fall off above size 3. Smaller squads will tend to get wiped more often, so after the first dozen or so turns I only use them in backwater areas for garrison duty against occasional stray barbarians, to take advantage of their lower maintainence cost. Putting them in the path of a multi-stack assault by the AI against one of your cities invites disaster, since they are more likely to be totally destroyed in the first engagement, leaving you short-handed in the following battles. With a decent combined arms stack of 8 size-3 decently trained units at level 3, I routinely stop 2, 3, or sometimes even 4 full stack assaults cold, occasionally losing one or two units in the process as they wear down by repeated combat.

By comparison, it is only in the relatively late game that squad size even becomes an issue in Spartan, since the cost of filling up to a 16 unit limit is already prohibitive until the larger empires finally begin to develop some serious industrial capacity. Filling up a 16-unit stack with size 2 or 3 units can bankrupt your empire, almost as soon as it steps into the field.

For me the problem is not even to build advanced barracks in each town. I don't like to lose my super veteran units (more then 5).

If you upgrade your barracks right away, you can have at least size two or three units before you can build anything better than Khepetj auxiliaries. Once swordsmen are available, the earlier units are pretty well obsolete anyway, regardless of size. Since no units start at anything over experience 3, and you can't upgrade your basic training camps until later, the early troops rarely get beyond level 4 before I've relegated them to some backwoods post.

I'd love to see an upgrade path in all of the games, so you could retrain the earlier units into more advanced types. Maybe for Legion II?