Make use of a step ladder or a regular ladder, if you find the window beyond your reach. You must ensure that the safety clip is on and also try to get someone hold the base of your ladder for your safety.
If you hire a professional to clean your windows, then find out if they are bonded possess all the required insurance documents. This will protect you against theft. There are cases of a window cleaner coming to your home and stealing, thus you have to be sure that you can get reimbursed.