I don't know what program in its right mind would arbitrarily require a 1.69GHz processor, but if that's what you need, that's what you need. As far as I can tell, you have an A6-3420M processor, and it can turbo up to 2400MHz under certain loads. According to this review, that turbo feature is hardly used, so you might be out of luck:
http/www.notebookcheck.net/Review-Toshiba-Satellite-L755D-14U-Notebook.73482.0.html You could try running in High Performance mode in Windows, or upgrade your processor to an A8-3520M, although that will make your base clock 1.6GHz, not quite enough. The gains from upgrading are mostly in the graphics department, so that likely won't help much.
TL;DR: You'll have to find some way to convince your CPU to use its turbo feature more.