While there is no limit to how many times you complete the exercises you will be working in a real Alfresco environment, not a simulation. Hence any changes you make to the system will be permanent. Most of the exercises are designed to be completed in a specific order, once you have successfully completed an exercise you should move on to the next.
Please notice that Virtual Machines will automatically expire after the period of time specified in the course description. This period starts right after course registration and it cannot be extended.
For reference, the expiration date of the VM can be found on the Lab Session (under the button). You will also be notified via e-mail few days before the VM expires. Please use this information to plan accordingly.