Fighter: Optional Class Feature

What are these?

The following list are class features that your dm may either allow you to have in addition to the features you gain from your class or they are options that might replace existing class features

Martial Versatility

4th-level fighter feature
Whenever you reach a level in this class that grants the Ability Score Improvement feature, you can do one of the following, as you shift the focus of your martial practice:

• Replace a fighting style you know with another fighting style available to fighters.
• If you know any manoeuvres from the Battle Master archetype, you can replace one manoeuvre you know with a different manoeuvre.