Can I upgrade to iPad native versions that are designed for full size?
This depends on each developer. Some are providing updates to their app that include optimized views for both iPhone and iPad; for example, the developer of Instapaper has decided to provide this as a free update. Others may release specific iPad versions; for example, a number of popular games will be available in iPad versions under a different name and presumably as a new purchase (sources: Apple leaks approved iPad apps, New apps discovered).