I have created a list using schema.xml and then i have created a list instance. later on i need to to add one column in the list schema which is not shown in the existing list instance. any idea how to resolve it?
The list schema is actually a template used at creation time.
If you want to update the schema of existing list, you will have to update the list itself (or the content type if the list is bound to a site content type).
There is no OOB way to do this, but here is a script I use in an upgrade process. My app use site content types, and list schema attached to this content type. The feature upgrade add the column in the xml declaration for new list, and the PS script add the column to existing list :
[Edit] You can reuse the same principle in a feature receiver which upgrades the lists...