What hardware do you have? What drivers are you running?
CPU
Motherboard
GPU
RAM
PSU
Cpu:Core 2 quad
Ram:4gb
Gpu:r5 240
That is some older hardware. I am not 100% familiar with it. Was the option available previously?
Yes it was avaliable
If that is an OEM prebuilt system, or card (dell, hp, etc...), then Overclocking was locked out and not included in AMD drivers.