Migration from dojo1.4 to dojo1.10

Hi Dylan and team
we are planning to upgrade/migrate our dojo1.4 based bank project to dojo1.10, to resolve few accessibility issues.
Could you please help us in answering the following questions…
first of all , is it possible to migrate from 1.4 to 1.10 directly.

if yes, How much it effects our current application? do we need to rewrite/revamp whole code… could you please let us know what all things we need.

if we rebuild whole app on dojo1.10 from scratch, is it better way?
Thanks
Venkata

Check this answer