how hard is it to change alt.on a slk230 mine is only putting out 13.2 volts & 6amps thanks

Under certain conditions, 13.2 volts and 6 amps would be correct. The voltage regulator senses battery condition and regulates alternator output accordingly.

I have never put an alternator in an SLK, but it is usually a very easy process. But provide us more information regarding output. Is this under full load testing? What are the test conditions?

Good luck,