Summarize:

As you likely stock your feeder with nectar, make sure to remove that before cleaning the feeder. You should simply pour the nectar down the drain. Once birds have fed in the liquid it will contain mold and other contaminants so do not save unused sugar liquid from inside of the feeders. You can make more nectar later with simple sugar and water or restock the feeder with store-bought nectar. If your buy nectar from a store choose the colorless kind, not the kind that is dyed red. Birds are attracted to the red feeder parts and do not need to ingest unnecessary petroleum dyes. The birds prefer cane sugar over beet sugar and you should never use anything except cane or beet sugar. You may need the manufacturer's guidelines to disassemble your feeder. However, disassembling a feeder is often self-explanatory. You can usually see the knobs and screws that must be undone to take the feeder part. If you are at all unsure, however, you should consult the guidelines to make sure you do not damage your feeder. If you lost the guidelines, you can type the name of your feeder into a search engine. You may be able to find a copy of the guidelines online. Some feeders, though, recommend using soap. Soap is not effective at removing black mold and soap is hard to remove without leaving residue that will harm the birds' stomachs. Usually, bleach is not necessary unless there is black mold in the feeder. For the most part, weaker cleaners like peroxide and vinegar work best as they're less likely to leave behind harmful residue.  Unless you see mold, opt for white vinegar or 3% hydrogen peroxide as your cleaner. Vinegar should be diluted with water. Use two parts water to one part vinegar.  You can also use simple dish soap. However, you should boil your feeder in a large pot of water to remove all soap residue because even a small amount of soap damages the stomach lining of the birds by attacking the stomach cells. If your feeder can't be boiled without deformation then don't use soap or use very little and soak the feeder in a large pot of water, stirring occasionally. Then rinse it very thoroughly. Fill up your sink with your chosen cleaner. Allow your feeder to soak for several hours. This will remove any toxins and make it easier to scrub off any grime. You will need a thin bottle brush to get into the various nooks and crannies of the feeder. Scrub the interior of your feeder with the bottle brush. You want to remove any nectar or sugar residue, as this can spoil and contaminate new nectar. Boiling the feeder, if it can be boiled without deforming, is a way of removing sugar residue without scrubbing. If you prefer not to scrub and have some mold, you can soak the feeder in an active chemical bath like vinegar or hydrogen peroxide. If soaked long enough, all biofilms (mold and such) should be destroyed. Remember that scrubbing does not always remove microscopic material.  After being soaked, residue should come off easily. You should not have to scrub with too much force. Rinse the feeder under hot, running tap water. Rinse each part of the feeder until the water runs clear. It's very important to rinse the feeder completely in order to keep harmful residue from getting into hummingbird nectar. Set the feeder in a dry, safe place in your home. Allow it to air dry completely before reassembling it and putting it back in place. How long this will take depends on the humidity of your region. It can take anywhere from a few hours to overnight.
Pour out all the nectar. Disassemble the feeder. Select a cleaner. Soak your feeder. Scrub down the interior of your feeder. Rinse the feeder completely. Allow it to dry completely.