Howto edit stars?

[m1omg]

Can somebody please tell me that how can I change stars's parameters?
I want to change Sun's parameters to that when it will be subgiant.

[selden]

The correct way is to create a new STC catalog for it which you put in the /extras/ directory: duplicate the entry that's in nearstars.stc and change the appropriate values.

You could edit nearstars.stc, but that's not a good idea, since it'll be replaced when Celestia is upgraded.