Hello, 

There are always big changes between Odoo version like:

• Model changes
• View and actions changes
• New widget use on new views etc ...

One example migrating between saas-5 and odoo/8.0 is the changes of WMS (stock, stock.move, quants etc ..) so data should be migrated. (not only programs and view). Odoo business is migration, so you have to solutions (or three):

1. use migration service from Odoo SA
2. Search for a partner and they can eventually make a quotes
3. Try to do it yourself by using community apps like OpenUPgrade or Anyupgrade, but this is not as simple as it should !

Thanks,