When does one become pure from menses if they exceed ten days while it usually does not exceed one week?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

What is mentioned in the question is what is known by the jurists as the change in menses. According to the most preponderant opinion of the scholars what exceeds the period of menses is considered as menses when this happens the first time as long as it does not exceed the maximum period of menses, which is fifteen days. If the menses exceed this period, then a woman should take into account her usual length of menses and whatever exceeds this period is considered as post period bleeding, and she should make up the fasting and prayers that she missed during this period which exceeded her usual menses. 

Allaah Knows best.