glRotatef(GLfloat angle, Glfloat x, GLfloat y, GLfloat z);
The Above function is what you need for your purpose. It " multiplies the current matrix by a rotation matrix", as the OpenGL documentation says. Here's how you use it-
angle is the angle you want to rotate. (Duh.) The next three parameters define the axis around which you would like to rotate. You input the x, y, and z components of the unit vector pointing in the direction of your desired axis of rotation. For example, if we wanted to rotate in the x axis, our vector would be [1.0f,0.0f,0.0f]. You can choose any arbitrary axis you want here. For our case, since we are doing 2D, we want to rotate around the z-axis, so we set x = 0.0f, y = 0.0f and z = 1.0f.
And as @concept3d mentioned, you need to specify that you want to make this rotation apply to the texture matrix, and he gives a way of tell OpenGL that.
Note that after setting the rotation with
glRotatef all things renderd after that will be rotated by that angle you specified. Be sure to set this for each object, if different rotation are need.
Hope that helps. Happy rotating!