My question is very simple, I want to turn off mirroring in the texture paint mode (I'm using Blender 2.74 and I have tried a few older versions). In tutorials I saw that there was a "Symmetry" tab, but I only have Brush, Texture, Texture Mask, Stroke, Curve, External and History.
This option is only available in the upcoming version, 2.75. It's not present in Blender 2.74 so there is no way to enable or disable it in this version.
You can either wait for the 2.75 release or if you want this option right now, download a release candidate version of Blender: