upgrade odoo 15 to odoo 16 sh

As a business owner, I need to upgrade my Odoo system from version 15 to version 16. The current Odoo version 15 I am using has custom developments built on top of it and I need assistance with data migration during the upgrade process. With all the custom developments built, the migration process is proving to be a difficult task to complete without help. I am looking for an experienced freelancer to help me upgrade my existing system and migrate all of the data over smoothly.