Remove 2.8 and dual boot 3.4 with Ubuntu

[gold_finger]

You do use the ISO file you downloaded, but you need to burn that to a DVD or USB in order to boot computer with it and install.  In your LL2.8 installation you can use the xfburn program to burn the ISO as an "image" to a DVD; or you can use the dd command in a terminal to make a live USB from the ISO file.  (See the Help Manual for dd command instructions.)

Is parted more accurate than gparted or is it only preference

You can look at partitions in GParted if you prefer that to entering terminal command.  It will show same info as parted command -- eg.  what is shown as /dev/sda3 with parted will also show as /dev/sda3 in GParted.  (I just happen to prefer terminal commands myself.)