If I have an iphone 6 will I be able to update my apple watch to watch OS 6?

No, not according to: watchOS 6 - Apple

watchOS 6 compatibility.

"watchOS 6 requires iPhone 6s or later with iOS 13 or later, and one of the following Apple Watch models:

• Apple Watch Series 1
• Apple Watch Series 2
• Apple Watch Series 3
• Apple Watch Series 4
• Apple Watch Series 5

An Apple Watch with watchOS 6 will not pair with an iPhone 6 or older.

There are already posts in this forum from users that now have to decide to give away their useless Apple Watch, put the watch in a drawer, buy a used iPhone 6s or newer iPhone, other. But their iPhone 6 can no longer be used with the watch