Do I have to upgrade when my free log quota is full?
No!
Every project you set up is assigned a free log quota of 500. When the free log quota is full, your StatCounter does NOT stop tracking! The oldest entries in your log are simply overwritten by new entries.
This means that you always retain an online history of the last 500 pageloads on your site.
Note that you do NOT need to reset your stats when your log is full.
StatCounter is happy to track your site for free for as long as you want... with one exception - if your site gets in excess of 250,000 pageloads per month this falls outside of our free plan. Unfortunately, it is not economically feasible for us to provide a free service to a site with this level of traffic. In this case we ask that you upgrade your StatCounter account or remove the StatCounter code from your site.