How to change the week for more lessons at once?

In case you have not defined a two or more weeks in timetable yet, you should do it now. Please, check this article:
How can I define weeks?

Now, go to menu "Specification - Change". New window "Change" will be displayed. You can leave all lessons selected or specify the lessons for particular subjects (1), classes (2), teachers (3). Select the mass change you wish to do (4) - in this case it will be "Change week".
Each selected mass change will have its own options. In this case you can specify how the weeks should be changed. Select your request and confirm with button "Change".