You are responsible for changing the lengths of contracts on your team page after resigning them. As you will be at the end of the year for contract length and age
To resign a player you take there Rating and divid it by 10 and then you multiply that by the number of years you would like to sign them for
Example:
Resign RB 90 overall to 6 years. 9.0*6=54 points
If you are extending a players contract it is the same.
For example,
Joe Blow QB 90ovr has a 3yr existing contract, you sign him to 3yrs. 3*9.0=27pts He now has a 6yr deal.