Beta testers who have signed up for Apple's beta testing program will receive the iOS 9.3.2 update over-the-air after installing the proper certificate on their iOS device.
Those who want to be a part of Apple's beta testing program can sign up to participate through the beta testing website, which gives users access to both iOS and OS X betas.
iOS 9.3.2, as a minor 9.x.x update, focuses primarily on performance improvements and under-the-hood bug fixes to address issues that have been discovered since the release of iOS 9.3. We don't know all of the fixes that will be included, but significant Game Center bug appears to have been fixed in the first beta, while iOS 9.3.2 beta 2 added the ability to use Low Power Mode and Night Shift simultaneously. No other outward-facing changes or immediately apparent bug fixes have been discovered in the first two developer betas.
Article Link: Apple Seeds Second Beta of iOS 9.3.2 to Public Beta Testers