Command + I (CTRL in Windows), inverting your layer will create a negative look (like back in the film days). This look will make the sensor spots more obvious even when in normal view they were hard to find. Once the image is inverted you can easily find and remove the spots no problem.
Do yourself the favor of saving time by having your sensor cleaned by a professional.
It is important to note that while this tip is great for removing sensor spots from your image, the problem is that it is after the fact. Which means that these spots live on your sensor now. Which also means that you are going to have to remove these spots from every single image you decide to print. If you like that kind of added, unnecessary work, then be our guest. I think PhotoNERDs has a dry, dirt lawn somewhere that needs mowing too. Get your sensor cleaned and don’t gloss over the fact that we advice having a Pro do it unless you are confident you can do it without destroying your sensor by doing yourself. A damaged sensor would mean your camera may need to be replaced as a whole, so proceed with caution.