Shalom and thank you for your question!
The difference between Giur, conversion, and Giur l’Chumra, conversion – to-be-sure, (or to be strict), is that in the case of regular conversion, the person converting was for sure not Jewish beforehand according to Jewish law. With Giur l’Chumra, there is a possibility that he/she is Jewish, but since there is doubt, he /she undergoes the process of conversion to be sure.
If the person already has a Jewish name, they may keep it, and if not, they should take a Jewish name.
If your question refers to an actual case, a proper Rabbinical Beit Din for conversion should be consulted. Only orthodox conversion is valid, any other kind only causes confusion.