Go on you tube there's a how to remove the head unit
I found it as I was looking to add a means of getting iPhone/iPod to the system
Found link
https://www.google.co.uk/url?sa=t&rct=j&q=lexus%20rx%20350%20remove%20radio&source=web&cd=1&ved=0CDgQtwIwAA&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DSnfwF2Hhvu8&ei=7sgwUoDfN4Sf7Abh94GACQ&usg=AFQjCNEL-R8h44XyhgIFAfzwdOXBHNgtuA&bvm=bv.52109249,d.ZGU