Now running Mint 15 and Windows 7. Trying to upgrade to Mint 16. All went well until I got to partitions on the installer. I did not want to install along side of dual boot nor erase all to install 16, so I chose "other". Instructions say choose "specify partitions manually (advanced )" when asked by installer - it does not say that. In small underlined print it says "advanced partitioning tool" for more control. I clicked on that and it shows a screen the same as a gparted screen. Like this :

/dev/sda format size used
/dev/sda 1 ntfs __ 491525 MB 55502 MB windows 7 (loader)
/dev/sda swap __ 8579 MB 0 MB

/dev/sdb 1 ext4 __ 248189 MB 4092 MB
/dev/sdb 6 ext4 __ 243336 MB Linux Mint 15 olivia
/dev/sdb swap __ 8579 MB 0 MB

Installations say select partition of current Mint, assign "/" to it and reformat it to "ext4". When I select the Linux Mint 15 line it shows " no root file system is installed Please correct this from the partitioning menu" Can someone please tell me how to do this step? I need to know this for now and future updates. Thank you.

Are you trying to install a new system or to upgrade the existing one? Looks like you are trying to update through install process that is a no no.
From a running system, Mint 15 in this case, you just run the program that deal with updates/upgrades.

Regards