Post a picture of your bike. Assuming its stock there should be two side covers. Those come off and behind then are air filter housings. Those come out. There is an H pipe between the two air filters and the carb with a connector in the H pipe that goes down to the breather port. Take that off. Once you take the H pipe off you can take the carbs out. You will have to remove the throttle linkage to take it out. I actually pull my carbs off slightly and pull them to the right. Once I have the carbs out of the frame on the right side I take the linkage off. It is easier for me to take off when the carb is off of the bike.
This link should be all you need when it comes to cleaning the carbs.
www.xs400.com/threads/carb-cleaning-carb-tuning-links.13321/
Once you have the carbs clean get a fuel filter for the carb. Something like this:
https://www.amazon.com/gp/product/B01ALCLRGM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
At this price you can afford to change them every year or every other year.
Let us know if you have any more questions.