The easiest way to get started developing SharePoint apps with LightSwitch is to sign up for a free trial of an Office 365 Developer account at dev.office.com. Because Office 365 has moved from preview to release, if you singed up for a preview account, you have until May 31st to convert it to a paid subscription. Doing so will save all your content.
You can use your MSDN subscription benefit to get a year free. Here’s a step-by-step slideshare by Randall Isenhour (@SharePointDev) from the Office content team.
I just converted mine and it took about 5 minutes.
For more details see the Apps For Office and SharePoint Blog:
Convert your Office 365 Developer Subscription Preview to a General Availability subscription to save your content
Enjoy!