how configured ramcache in Big-IP 5250

Hello people!

i have a problem, i want to configure a ramcache but i am reading about it and i need to configure a ram cache with size of 400Mb but in the manual described a parameter called “Maximum Cache Size” in the profile of http but in my setting dont exist this parameter at least not in the web interface. I have a Big-Ip model 5250 . somebody have a idea ?