Unable to change from 14th to 7th
If you can, with the chain in one of the middle cogs in the back, shift to each of the front chain rings then your front derailleur is likely in proper alignment and adjustment. This question and answer cover how to adjust the derailleur if you want to learn how to do it yourself.

What you are describing, shifting to small ring in front and small cog in back, or big ring in front-big cog is called "cross chaining" and should be avoided. If you ride cross-chained it causes:


Significant stress on the chain, and may cause failure.
Added friction and wear on the drive train.
Possible derailleur failure if you cross chain "big to big"