Does anybody know how to withdraw a I-140 petition? Thanks.

I ted an EB1a application myself and got a REF recently. Since they
: required too much evidence and I already have an approved EB2/NIW with the
: priority date Feb.2006, I am thinking to withdraw my EB1a petition. Dose
: anybody know how to withdraw this petition and will my 485, which was
: ted simultaneously wiht EB1a petition, be automatically get invalid
: after I withdraw my petition? Thank you very much in advance.