I haven't had to renegotiate any contracts yet, since they are all one month RL (1 year) contracts. I do see an option for each player to be set to "auto-renew contracts." I'm assuming when a contract is coming to an end I'll be given a warning.
Here is the dialog that comes up when I select to "auto-renew" a player's contract:
It appears that you can only do this for 5 players, which will make them "protected." I'm not really clear on this (there isn't exactly a manual for the game at this point". I'll try to detail what I learn about contracts as I learn it.