I have a lot of Kennedy Half Dollars

[Rainbowmountains1]

Do you know what years are worth the most ?

[Gill]

This question would be better on the Coins and Bank notes forum OP.

[poppa501]

1964 are 90% silver and are worth the most. 1965-1970 are 40% silver. The rest unless they are errors or such aren't worth much more than face value. Of course everything differs according to condition.
You might want to check http://www.numismedia.com/fmv/fmv.shtml