If the spots are on the image, then the dust is on the sensor or lens. If the lens, it is probably the real element (closest to camera) since spots on the front lens don't show up since they are so out of focus. If it is the sensor, use a blower (camera hole down may help to avoid more duct but be careful not to hit the sensor with the blower). A simple blower will clear 95% of dust or lint that I might pick up.
If the spots are in the viewfinder but not the image, it is likely the mirror, viewfinder/prism or lens. My recommendation is to use a blower or leave them.
I have high-end Canon camera and lenses and I never do what many folks are recommending. I do not clean the mirror except with a blower bulb, not a blower brush. The coating on the mirror is very delicate and sweeping it with a brush or swap is looking for trouble. You can easily damage the mirror or coating, for absolutely no reason. A couple specs of duct on the mirror does not affect image quality.
You can have dust on your pentaprism, the glass block in your view finder. Look up above the mirror. It has a fine focusing surface. Again, this surface is easily scratched by grit or dust so I would simply use a blower bulb, then leave it.
You may not need to clean your sensor except once a year or much less. I shoot in a great variety of dirty and dusty conditions and I rarely clean the sensor more than once a year. Copper hill is a good DIY but if you are not comfortable, have it done. There is a good shop in Manchester (Hunts) that can do it pretty cheap.
Lens cleaning - always use blower first. The lens has an anti-glare coating that can scratch with a cleaning rag or swab. Use blower first. After that, breathe hot breath on the lens to fog it and then light circular wipe with a new lens tissue or clean microfiber cloth. You will almost never need anything else to clean your lens.
Many people have permanently scratched or damaged their sensor, mirror or prism trying to remove a spec that never affected their images. I have heard many say they clean their sensor or mirror all the time without damage. Take a look with a lighted magnifying glass and you might see serious scratches or worn off coatings.
Hope this helps.
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