If you want to use your own G+ image, do the following.
1. Get your G+ image (16 and 32 px), name it as “googleplus”
2. Go to wp-socializer/public/social-icons/ and add the icons in the respective folders. (Have a backup & Replace the originals)
3. In the admin page, Buttons->Social icons and set “Use sprites” to no. Then save the setting.
Thats all !!