This is a very generic question and I do not know what exactly the problem is. Do you mean that you can not modify them? One thing that comes to my mind is maybe your geometry is set from the scripts under model (which can be found under Objects Tree). In this case software will not allow you to modify them from their edit tab.
If you are new to the software, you can take a look at getting started examples and watch our webinars.
Also, you can take a look at grating coupler example that might be similar to what you want to achieve.
If you still had a problem, please clarify the problem and provide references, and I will be glad to take a look at your simulation file.