Why was Abrahams name changed and how was it changed?
Nancy, Abraham’s original name was Abram which meant “Exalted Father” but after making his covenant with God, God changed his name to Abraham, which means “Father of many nations” see Genesis 17:5.
The Lord changes people’s names to depict that the new relationship that they have with Him. Sarai becomes Sarah, Jacob becomes Israel, Simon became Peter etc. It was typical in Christian missionary work to have converts take a Christian name, particularly if they had been named for pagan deities. This new name was given to them at their baptism when the priest asks for their Christian name. The person was then claimed for Christ and that is why some refer to baptism as christening.