Step-by-step explanation:
The teaching remains the same and till date there is no amendment in their holy book as they consider it to be God's language. Although, they have a rule book also which guide people belonging to Islam how to live in a religious way in day to day life but to be precise that too is outdated now.
The only change which can be observed is in language. For example in India the Islamic people speak Urdu which has its origin from Arab language. Rest things are same throughout.