Mortgage and release

our Company had taken loan and created a simple mortgage of property (movable & Immovable in favour of Bank ). after 2 years the bank gave more higher loan but asked the mortgage to be created (for current loan including previous loan ) in favour of a Security Trustee. Now the charge held by Bank to be released and fresh charge to be created in favour of trustee. what should be the document for release of charge by Bank ? is it deed of release or deed of re-conveyance ? again for fresh charge in favour of Trustee we have to execute fresh Indenture of Mortgage with Trustee. is there any alternate mechanism which facilitates transfer of mortgage interest from Bank to trustee. appreciate valuable inputs from learned members.