Very easy, 5 min job.
http://www.ebay.co.uk/itm/BMW-Z4-E89-20W-CREE-LED-Angel-Eyes-Marker-Upgrade-Bulbs-H8-Xenon-White-Look-Set-/321046834669?pt=UK_CarsParts_Vehicles_CarParts_SM&fits=Car+Make%3ABMW%7CModel%3AZ4%7CPlat_Gen%3AE89&hash=item4abfe1eded
BMW Z4 E89 20W CREE LED Angel Eyes Marker Upgrade Bulbs H8 Xenon White Look Set.
The other ones that caused me radio noise, even with the suppressor upgrade were cheaper.
http://www.ebay.co.uk/itm/BMW-H8-Lux-20W-LED-CREE-Angel-Eye-Bulb-Markers-for-BMW-E82-E89-E90-E92-/221253253120?pt=UK_CarsParts_Vehicles_CarParts_SM&fits=Car+Make%3ABMW%7CPlat_Gen%3AE89&hash=item3383b8b800