Laravel data migration to new structure

We are planning a major database restructure and instead of "Create" all the migrations are "Alter"-ing already existing tables.

For example:

There's table users that holds a column, e.g. role.

After running migrations this column will be dropped and table "Roles" will be created with a hasOne relationship (just an example).

How should I approach converting the old data into the new structure as seamlessly as possible?

via Chebli Mohamed