A simple way is to write:
-std=c++11
in the Other Options section of the compiler flags. You could do this on a per-project basis (Project -> Build Options), and/or set it as a default option in the Settings -> Compilers part.
Some projects may require -std=gnu++11
which is like C++11 but has some GNU extensions enabled.
If using g++ 4.9, you can use -std=c++14
or -std=gnu++14
.