"taghir dadan" is a transitive verb which means it needs a direct object: (chizi ra) taghir dadan u do sale pish name khanevadegie khod ra taghir dad. He/she changed his/her last name 2 years ago. but "taghir kardan" is an intransive verb and doesn't need any objects u bad az ezdevaj kheili taghir karde ast. he/she has changed a lot after his/her marriage.

As Saeede Mrt said, it's the matter of being transitive or intransitive; tagir dadan: This book changed my life. meaning: (in ketab zendegi man ra tagir dad) tagir kardan: My life changed. meaning: ( zendegey man tagir kard)

taaghir dadan is transitive and taaghir kardan is intransitive.