Hi @shubham2025 ,
Please refer
Seeking Assistance for ERPNext v14 to v15 Upgrade - #2 by nilpatel42 or
https://codewithkarani.com/2024/01/03/how-to-upgrade-erpnext-from-version-14-to-version-15/.
Also check frappe official document on migration Migration Guide to ERPNext version 15 · frappe/erpnext Wiki · GitHub
Thanks,
Daizy Modi