Your rifle is a Marlin 336. To unload- with the rifle pointed in a safe direction, and your finger AWAY from the trigger, operate the lever. This will retract the bolt, and eject any cartridge in the chamber. When the bolt closes, it will load any cartridge that is in the magazine. Continue to operate the lever until no cartridges eject, then check by eye to ensure the chamber is empty.
1958-1961....
I believe you have a Marlin 35 Cal. Model 336 CS rather than a C5. Look again.
Your rifle was made by Marlin for Sears, but used a different serial number sequence, making it difficult to date it precisely. The JC Higgins name was only used on the model 45 from 1958 to 1961. By the way, that is a really good deer rifle.
Marlin
100-400
100-400
It is a Marlin 336 carbine as made for Sears.
35-80
35-80
1950
your marlin model 336sc(sport carbine) was made in 1951.
1981