You can get adapter looms to convert the wiring to fit the radio of your choice.
I used Autoleads ones in my old sierra and my cossie.

There are 2 different kinds of adaptor looms. One for the amp under the head unit and a longer one for the types where the amp is in the n/s/f footwell.
I assume yours is the first one.

When you have fitted the new head unit, the amp below will already be disconnected so just leave as it is!

Job done!