You can upgrade your site through extension manager. From Joomla 1.6 ,it has build-in update functionality in extension manager. For more detail see this tutorial :
Upgrade joomla site 1.7 to joomla 2.5 [duplicate]
Вопрос
How to upgrade a version of joomla web site from 1.7 to joomla 2.5
Решение
Не связан с StackOverflow