By default, SDK 3 is configured to generate projects using the most recent version of ACS and Share. You can easily change one (or both) versions by simply updating the pom.xml file in your project. The compatibility of these versions is up to you, however you should check in advance the right versions to use.
Note that if you used the Share JAR archetype you will only see the alfresco.share.version property. Otherwise, for the All-In-One and Platform JAR archetypes you will see both properties. So if you need to generate projects using different versions then these are the properties to modify.
Use the links below to see more information on how to use the different supported versions.