You can't directly, however there is a way that this can be achieved. In Task Scheduler, highlight the task in question. Click on Export... and choose a location to save the file (Desktop is as good a place as any). Click Save. In Windows Explorer, browse to the location where you saved the file. You can then rename it as normal. Back in Task Scheduler, click on Import Task... and browse to the now renamed file. Click OK. Now highlight the original task (remember that there will now be 2 tasks, one with the original name and one with the new name) and click Delete.
All other task properties, apart from its identification name, can be changed/modified directly.