Depending on what year/model you have it can range from very easy to a royal pain. If it is just a standard indash, then just replace it. You may want to bypass the fader control by re wiring the speakers. but it should be a plug and play issue. If you do not have a real high power indash I would just hook it up should not take more than 45 min.

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Currently
1991 Mazda Miata 174000
1991 Subaru 189,000 Winter beater

got rid of:
1984 VW Vanagon 195,000
1976 350SE Euro 185,000 KM
1973 280SE 4.5 (boy do I regret that)
1980 280SE European W126 4 speed manual (miss it)
1989 BMW 735iL 119000 (good riddance)