When you reset your statistics of your cellular data, will it reset how much data you still have left? Or will it just change the number of data and you would still have so much left?

If you have 6GB left on your cellular plan, you would still have that much left no matter what you do with the statistics. The statistics are just a running count of how much data you have used since the last time you reset it. If you don't reset it, the number will just continue to grow and as months go by may far exceed whatever your monthly plan has. It doesn't know what your plan limit is. I used to have a reminder in my calendar to reset it each month on the same day as my plan renewed, just so I could keep the two in sync.

Resetting statistics does not impact how much data you have left. It is there for your convenience to estimate how much data you've used (and I say estimate because this only accounts for data that has successfully been received by your phone, and the data your cellular carrier says you have used is usually just a little more than this).

You would still have 6gb left. It just resets the recording of elapsed time of usage of the LTE.