currently i am working with ERP-Next V-8, too much customization done in same version.but want to upgrade latest version.
pls help me, How to do that and what are the steps? without loss my data and custom changes.
Please share as how have you done this customization? Have you added custom scripts, field or custom app? Customization of this sort should not be a problem. But if you have edited the source code or edited core doctypes itseld, then it will be over-written in the upgrade process.
Does that include simple edits to core doctypes, like making a field mandatory?
All types of edits.
If any changes are needed in the core doctype, it should be done via Customize Form / Property Setter. If done that way, then it will remain after the upgrade aswell.
If your changes are linked with git commits I think it may easy to checkout to the last commit before your customization and then you can aggregate your customizations in custom scripts and custom fields in a custom app for your purpose, it may take some time but it will put you on the track to be able to update your frappe and erpnext without conflicts.