Hi,
Never done this, but it's covered in the eLearn service manual. You can get eLearn from the download section of the forum.
Does not look difficult, but a fair amount of work. According to eLearn you need to remove the cross beam cover, grille, both wheelarch liners and undertray.The covers and liners have plastic rivets that are expanded by a pin in the middle. You push the pin trough and then pull the rivet out. One some the pin will disappear into a chassis cavity are are a pain to recover. They are cheap so it's worth buing new ones in advance. I've bought some that are intended for Volvos, ebay item 281623532839 that have a moulded center pin that does not drop out the other side.
HTH,
Robert G8RPI
Croma 1.9 16V Eleganza.