Replacing generic RECEPTACLES

Or does it have to be only a 15 amp receptacle on a 15 amp line. 

Also can anyone answer my question about elizabeth? Thanks. 

Googling 20 amp duplex on 15 amp wires NEC says no. The NEC is not the wire police. They are guides used by electricians as to what they can and cannot do since they are contractors and THEY have legal and liability concerns. For the apartment dweller, or homeowner. Those concerns are not a law, You cannot go to jail for using a 20 amp duplex on a 15 amp line! But in the event of a fire caused by your 20amp duplex.. Your insurance company may have problems... The fact is the breaker is going to trip (15amp) before your 20 amp duplex gets to flow 20 amps, over heating the 15 amp wiring in the wall and box.
So the answer is technically no, you cannot use that 20 amp duplex on a 15 amp branch, and no electrician will install it (maybe)... But YOU CAN, if you want to break the rules, knowing the consequences. Anyway, If you cannot sleep at night knowing you have done this, then do not do it. I have no problem with using a 20 amp duplex on a 15 amp line. (BTW I use a 20 amp circuit for my system)

elizabeth...Thanks...But can u answer me this? I thought it would be dangerous if you used a 15a receptacle on a 20 a line, not a 20a receptacle on a 15a line. In my opinion it would be less voltage going into a 20 a receptacle on a 15 a line. But what do i know. 

elizabeth...Also so u are suggesting to use a 20a circuit for my 15 a cdp?