Berserker Upgrade

Hmm... could someone plese explain how I might use the Berserker upgrade to say, change a Swordsman into a Captain (for examples sake) Whenever I try both the original units and the advanced units are buildable, and when I reseach the upgrade the basic unit dissapears.

You must make sure that the abillity have the upgrade to be required, and make the original unit to have the abillity.

I think the advanced unit needs the upgrade listed under "techtree - requirements" examine the stats of the troll berserker (it's under orc - melee - special) to see what must be set for it to work.

Thx, I'll try as soon as I get back from vacation