The migration guide from 1.7 to 2.0 should help you with the migration. Although we have a few breaking changes in 3.0(listed here), there should not be any major change between 2.0 and 3.0. Please let us know if you have any issues upgrading to the latest 3.X version and we can help.
We strongly encourage you to upgrade to the latest version because it includes a ton of new features, broader platform compatibility, better performance and revisions to address the great feedback that customers have given us over time. In addition to that, the 3.X libraries also support the 2013-08-15 Storage REST version that introduced all these great features.