There are some new features in Spring Boot 1.3 to do with OAuth2 clients and servers and Spring Security OAuth2. Some of those features were ported from Spring Cloud Security and hence were in the Angel release train of Spring Cloud, but are not in the Brixton release train. This article helps you navigate the changes and update any existing apps to use the new features.
If you are not using Spring Cloud you should be able to just change the version number of your Spring Boot dependency. Since some of the OAuth2 features migrated from Spring Cloud Security to Spring Boot in 1.3, it is likely that things are slightly more complicated than that. A separate article deals with upgrading Spring Cloud apps from Spring Boot 1.2 to 1.3. If you are using the Spring Cloud Angel release train then you should consult that article for details of how to manage the dependencies (independent of any specific features).