powerpoint london - Presenting on a 16:9 screen

Do you mean you can change the size of your slides? If so, yes, you can change the size by going into File>Page Set Up> there is an option there in the dialog box for "Slides Sized For" and there is a drop down menu which if you can't find the correct one you want the last option is custom and you can input your required dimensions.

Hope that helps, good luck

Tracy