As Geronimo mentioned, there is a $5 "downgrade/sidegrade" fee. If you increase your programming (not just end up paying more a month--i.e. drop the Sports package and pick up HBO) there is no fee. If you drop programming just before the "drop" is forced on you or Dish is forced to drop a channel/package (locals), there is no downgrade fee. Also, the downgrade fee can be waived on a case by case basis. For example, I dropped the annual AT150/Mega Movie Pack and picked up the monthly America's Everything Pack (same number of channels, but it is considered a downgrade--annual to monthly), but since there is no annual package for AEP, the fee was waived by the CSR without my even having to ask.
Finally there is a $10 downgrade/sidegrade fee on adult programming. It seems that some wisecrackers out there figured out that it was cheaper by al long shot to subscribe to an adult channel for a day, record all the movies that day and unsubscribe (about $1 for a day's subscription to the channel +$5 downgrade fee as oposed to the $10 single movie PPV price). So Dish imposed the $10 downgrade fee on the adult channels to prevent the increadible churn on these channels (and loss of revenue).