I am a beginner to dark souls prepare to die edition. I got the zwehilander sword. I wanted to know If I upgrade that sword, will it support to finish the game. I am in undead burg and I have a titanite shard. My stats are 14 strength and 13 dexterity as a warrior.
So each weapon has its own style of scaling depending on how you want to build your character.
Zweihander is a strength based weapon meaning the more you scale this up the higher damage output you will have
According to the DarkSouls Wikia it has a 60% Strength Scaling and a 26% Dex scaling, that is just the Basic version.. Zweihander +15 325/0/0/0 C/D/-/-
The base version of this is the best version of the weapon so I wouldn't recommend enhancing it.
Usually most people I've seen stop around 40 strength as the scaling return starts to become minimal.
Give it plenty of practice and you can complete the game many times over using any weapon.
Dark Souls is one of those game where you have a lot of flexibility and you can choose whatever you like doing, stick with it, and it will be end-game viable, regardless of whatever weapon you choose.
What you should avoid is a "jack-of-all-trades" type build, because you'll end up being sub-par in everything.
If you like your weapon's move set, then by all means, focus on it and you'll do fine.