I would like to amend an existing lien I had placed for an increased amount.

North Carolina mechanics liens can't be amended. The NC lien statute specifically disallows it, actually. § 44A-12(d) of the North Carolina lien statute states: "A claim of lien on real property may not be amended." 

However, the next sentence goes on to state "A claim of lien on real property may be cancelled by a claimant or the claimant’s authorized agent or attorney and a new claim of lien on real property substituted therefor within the time herein provided for original filing."

So, while North Carolina mechanics lien claimants cannot amend their lien claims, claimants are able to cancel their original lien filings and replace the old lien with an updated lien - as long as the lien deadline hasn't passed.