Can't upgrade first Survey Ship

The survey ship is a medium sized ship, so you won't be able to refit it until you have other ships with medium sized hulls.

Not so sure , I was not able upgrade "defender" design either (in compain) even I had all the advenced tech.
I mean I could upgrade the ships but not the design (wanted change the weapon).
The "Upgrade" button in ship design screen is just disabled for it.

Is it intended ? - If yes then it's very unconvinient , at least an option to base a design on some current design required !

That's intentional. You can't alter the original ships designs. What you can do is create a new design for the same sized hull. So, for example, you can create a new Survey ship (once you have the necessary techs), and then on the main gameplay screen select your original Survey vessel and click the Upgrade button. You can then decide which of your medium hull designs to upgrade it into. 

What if you want to create a new survey ship with improved speed, range, and/or sensors but keep the eye candy of the original? What is needed is the ability to copy (even the original ship designs), modify, and save a ship design under a new name. See my early post Link, many others agree!

I had a valid design for it (small hull this was at least shown in the upgrade list.), and for self created the upgrade to this design worked....

Just for the Survey ship he was saying upgrading to Railgunner 2...
estimated time 0wk
costs --- (for all offered firms and direct buying)

I think this one is really important as the first survey ship will have the best opportunity to become one of your stronger ships (at least at the start of the game) that ship had at least 28 hP were next best ship had only 10...