Description: Outdated units seem fated to be used as cannon fodder at present, with seemingly no path to upgrading them being available? Perhaps this is already supported but is not obvious in the UI?
Suggestion: Add an "Action" button to standard units called "Upgrade" or "Change Equipment".
This button should be greyed out while the unit is in the wilderness and only active whilst in a town.
Clicking the Upgrade button would then bring up the Unit Design screen with your current unit designs listed. At the top of the screen it would say "Upgrade to:" rather than Troop Roster. At the bottom of the screen the buttons would be "Upgrade" (performs the requested upgrade) "New" (opens unit design window with existing unit weaponry loaded) and "Cancel" (cancels the upgrade process).
If the player chooses to upgrade a unit it should then be unavailable for a period of time while the troops receive their new equipment and training. It should be a shorter time and a lesser cost than an entirely new unit would be, but the unit would retain any experience it has gained, any existing enchantments that might be on the unit, etc.