Bike not changing gears correctly

Cable tension Sent from my iPhone using Tapatalk

If the tension does not work takes look at the detailer. Mine had a similar problem and what I found was I bent it ever so slightly, you could see the chain was riding on a slight angle and it would do ghost shifts. In 6 and 7 but not in 5th or Iower,l was able to straighten it out and the chain did not run at a slight angle no more so no more ghost shifts. Hope this will help

http://sheldonbrown.com/derailer-adjustment.html

Check that your cables are tight when in the smallest cog. If you can't retune it yourself, I think you should take it to your LBS and ask them for a quick lesson as the fix it for you, most wont mind if they're not busy. Also check out youtube for tutorials.