Intellij error: usage of api documented as @since…, Usage of API documented as @since 1.6+..

To get rid of the first one, you need to open up

File -> Project Structure -> Project Settings -> Modules -> "Your Module Name" -> Sources -> Language Level

and change that to the desired level i.e 1.8 or the Project Default language level

To fix the second one:

  1. File > Settings > Build, Execution, Deployment > Java Compiler
  2. Change Target bytecode version to 1.8 of the module that you are working for.