Why My android device show less RAM and Slow at Jelly bean? I bought a new Samsung galaxy S Advance(GT-i9070). It came with Gingerbread. It was actually a phone with 768 RAM. I clearly verified this with the shop when I bought it. Last day I upgraded my phone to Jell bean with official Russian firmware and reset to factory default settings. But now the phone seems very slow . Also full RAM Capacity seems 521 MB at Application manager. All applications are now consuming  memory from total 521 MB memory.
My question is- where is remaining memory? How can I obtain the remaining memory to speed my phone? Some people on the web say to root the phone, install ROM manager etc. Are these approaches good? Please give me a solution
I'm also using the same  device. Also upgraded to jelly bean.
Well, to your above queries, just remember that higher RAM usage in jelly bean is actually supposed to "utilize" the device properly. Logically, we buy device with high RAM for what? So that we get faster performance. But there is always tradeoff between performance and features. Jelly bean offers more features but takes more RAM.

Regarding rooting the phone. It  is always a grey area. while rooting voids device warranty, it also enables user to  control almost every aspect of the device. But do it if you are willing to invest time understanding the intricacies of rooting.

cheers!