You can soak your glasses in the dish soapy water for a while. Then rinse them under the clean running water. In this way the dirt on your nose pads will be removed. However, if your nose pads turn yellow or green, it is hard to clean them. You's better go to the kit stores to get a new pair of nose pads which are similar to the original ones. Then you can replace the nose pads with the little screwdriver on your own.
The nose pad on the eyeglasses will get dirty and appear yellow if you not clean it for a long time. Here are some tips to help clean your nose pads:
Get a clean washcloth that doesn't produce lint. Then, use a small amount of water on a small part of the washcloth, so that it is damp. And leave your nose pads all wet. Next, Wipe it around the nose pads for as long as you'd like until most of the dirt is gone. At last, use a dry clothes to fry your nose pad.
Or if you don't like to do it, you can take your eyeglasses to your local glasses shop to have them clean it.
Firstly, remove the nose pieces carefully if you are able to. Some nose pieces are removable with a screwdriver made for eyeglasses; it depends on the frame design. If you do remove the nose pieces, make sure you keep track of screws and any other associated parts. Secondly, Dust the nose pieces off with a clean, soft cloth to get rid of any excess dirt or grime. Thirdly,Put a bit of mild soap onto a wet, clean, soft-bristled toothbrush. Scrub the nose pieces with the toothbrush. Rinse them clean and dry them with a soft cloth. At last,Dip a cotton swab into rubbing alcohol. Run this over the nose pads to disinfect them. You can do this either while the glasses are still connected to the pads, or after you have removed them.