Changing the head unit
In most conventional cars, you can easily change the head unit by pulling out the old one, buying a fascia adapter and a wiring loom adapter (typically from Autoleads) and plugging in the new head unit. Unfortunately the Civic head unit is a main hub in the car's communication bus, with incoming and outgoing connections from other bus hubs.
Keeping the display working:
The climate control and clock display will not work if you just remove the original head unit.
The convention is to install the new head unit (transferring the speaker wires from the old to the new) and then to leave everything else connected to the old head unit. The old head unit then has to be hidden away somewhere, typically behind the dash, unless you want to create even more work and cost.
If you do not want to retain the original head unit, you need to change the display for one used in a car with no radio and make some new wiring. See this post.
Another solution for removing the original head unit and still have a working display is to fit a solution as described in this thread.
The Audio connections on the standard HU are not ISO.
Pocket under the radio: 39116S30G01
Fascia (LHD): 77251SMGG00ZA
Fascia (RHD): 77251SMGE00ZA