The ringed spots are unlikely to be dust. I suspect water spots. Tim Campbell suggests oil. If you really want to know what they are, you should examine the sensor with a loupe. Regardless, you will likely need to clean the sensor with wet swab.

I disagree with having someone at a camera shop clean the sensor for you because it's such a simple process. However, you might have to visit a shop to buy the swabs and solution.

0. Purchase a sensor cleaning kit. Consider one that uses a low-alcohol solution.

1. Read the instructions that came with the sensor cleaning kit.

2. Read the instructions again.

3. Enable sensor cleaning mode to lock the mirror and open the shutter.

4. Use a dust blower to remove any free dust.

5. Read (again) and follow the instructions that came with the sensor cleaning kit.

6. If your kit has dry swabs, you may use distilled water in the final pass. This is usually unnecessary. Also, please refrain from serving large amounts of liquid to your camera.

7. Turn off sensor-cleaning mode.

8. Check for remaining dust with a plain, diffuse background and lens set to F22-32. It's normal to have a few small spots left, and it's a losing battle to attempt to remove every single spot, especially if all that's left is a single 2-pixel wide spot a corner. Most dust spots will not appear in photos taken with apertures larger than F8.

The ringed splotches are unlikely to be dust. I suspect water spots. Tim Campbell suggests oil. If you really want to know what they are, you should examine the sensor with a loupe. Regardless, you will likely need to clean the sensor with wet swabs.

I disagree with having someone at a camera shop clean the sensor for you because it's such a simple process. However, you might have to visit a shop to buy the swabs and solution.

0. Obtain a sensor cleaning kit. Consider one that uses a low-alcohol solution.

1. Read the instructions that came with the kit.

2. Read the instructions again.

3. Enable sensor cleaning mode to lock the mirror and open the shutter. Consider using a room that has had an air purifier running for several hours.

4. Use a dust blower to remove any free dust.

5. Read (again) and follow the instructions that came with the sensor cleaning kit.

6. If your kit has dry swabs, you may use distilled water in the final pass. This is usually unnecessary. Also, please refrain from serving large amounts of liquid to your camera.

7. Turn off sensor-cleaning mode.

8. Check for remaining dust with a plain, diffuse background and lens set to F22-32. It's normal to have a few small spots left, and it's a losing battle to attempt to remove every single spot, especially if all that's left is a single spot a corner. Most dust spots will not appear in photos taken with apertures larger than F8.