An iteration is a concept used within CMS Projects for the purpose of organizing issues into iterations.
Bring the iteration you want to rename into view and click on it. The Properties will display to the right. There, you can change the Name.
Simple Example View Configuration
<View> <Iterations/> <Columns> <IssueIDColumn align="right"/> <NameColumn width="300"/> </Columns> <Filter> </Filter> </View>