The reason R-signals appear stronger is because the common reference is located behind the left ear, and so the signals from the electrodes that are further from the reference appear to give higher power of readings.
Typical recording references for EEG data are one mastoid (which is implemented in SMARTFONES), vertex electrode (Cz) or linked mastoids (R4-L4). In order to re-reference the recordings to vertex electrode, you simply subtract Cz from all other electrodes. Alternatively, in order to re-reference to linked mastoids, you should subtract (R4+L4)/2 from all the electrodes. In both these re-referencing systems, your signals will appear left-to-right symmetric. We most commonly use the linked mastoid re-referencing, simply because we wish to keep the Cz recording in our data-sets (in case of vertex re-referencing, you will get 0 on the midline channel, and you cannot use this data in your processing).