renaming leaders

[Epaminondas]

Frostmourne27 said:
right click on the command in the main window. this brings up commander info. If renaming is on, you can press 'R' to open up a text box to type the new name. Note that the R is capital (lower case won't work) and that if you leave the input box blank and press ok, it keeps the previous name, which is handy if you do it by accident and don't want a commander named Ned the Fire Mage or whatever.

How do you ensure renaming is "on"? I tried this on my game and it said something like "renaming is not enabled"?

Thanks in advance.