Apple Watch series one update 4.3.2- at least 6
I have an iPhone X and an Apple Watch Series 1 running 4.3.2 is like to update it
Apple Watch, watchOS 4
Is it a first generation or a series 1 - they are different.
First generation OS 4.3.2 is the newest available
Series 1 OS 6.3 is newest
Look in iPhone, Watch app, My Watch tab, General, About and check out the model
You will need t look in wikipedia to work out which you have.
To check or update use the iPhone paired to it and go to iPhone, Watch app, My Watch tab, General, Software update and see what is available.