How to update version if changes are made directly to core files

Currently I am using ERPNext version 14 Frappe Version 14. now i want to update to version 15 but i have made some changes to the core files. so can anybody provide with a solution to how to do version upgrade and keeping the data and scripts working.
i help will be appreciated.

Hi @Abdul_Samad,

If you have a suggestion to update the main code and it’s possible to override it, please do so in a custom app. We don’t recommend adding code directly into the main functionality. However, if you can’t override it in a custom app and it’s necessary to change it for version 15, you’ll need to save each change separately. After updating the version, review each change individually and add your old changes if needed. But again, we advise against directly modifying or adding code to the core.

Thank You!

Thanks for your response.
I have custom app but initially by mistake i made changes to core file and honestly i dont even remember where i have made changes so i was thinking to have a fresh instance of version 15 and restore backup from version 14 to new one is it possible. i have data in account, HR , payroll, manufacturing module. or how can I
move data to new instance.

Restore the v14 database in v15 and migrate it.

Check the post, for the restore.