Thanks for replying John !! I knew someone would quickly bring this up & thanks for getting it out of the way !!! His is way beyond its EOL, but I do not consider that any problem just because there are alternate sources for the older versions. I am actually still using 12.04 in my older NB and both 16.xx & 17.xx in a desktop PC - and I really enjoy 12.04 very much despite its being so very old by most folks' measure. Having explained this - my question in the OP here stands & I'll greatly appreciate any helpful pointers in moving forward with this. Thanks.
I know you are looking for ways to upgrade. However - here is my two cents: backup his settings/data, clean install a LTS version 16.04.3, which will reach EOL in 2021. Upgrade is easier for the moment but may have issues in the long run.