You really should try searching. This topic has been covered dozens of times in this forum.
Here's the factory procedure.
http://deneau.info/ls/s6x~us~en~file=s6x33014.htm~gen~ref.htm
Note that you will also need to know exactly how to bleed the air out of the system after you do this. This has also been covered many times in the forum.
http://deneau.info/ls/s6x~us~en~file=s6x33004.htm~gen~ref.htm#extract_142