Its too easy. just burn the ISO file on DVD and boot it from DVD.
it will boot up like windows boot and a screen will come up which will have 3 options: namely
1. Install with clean partition (under this category your HDD will get formatted entirely). under this option just put the number 1 and click on OK. it will ask for the drive size. first for drive C and then D. the Lenovo_part (OEM reserved partition under each category will automatically is made automatically with all OKR files and folders with the partition size=14.26 GB)
2. under this option your C and D drives will remain unchanged, only the OEM reserved partition will be formatted and build as factory default.
3. I have not checked this option.
I have checked the option 2 while I had already made the LENOVO_PART reserved partition under option 1 and disrupted the contents of this hidden partition to check if it is reset. so it has been reset to default under option 2. but I do not know if option 2 makes Lenovo_part partition keeping other partitions intact especially system partition C.
I think if your HDD do not have any LENOVO_PART oem reserved partition or if you have deleted it accidentally then you have to chose option 1.
a request once again. please report me if any one has lenovo Ideapad z570 notebook with factory built lenovo_part oem reserved partition. then I will guide you to make it open and again hidden. by opening you can copy the contents of it for others users and I will be the first one probably.