In the right hand pane you can see the number of invocations, the source block, i.e. the block that triggers the monitor execution, and finally a description which is the doc string that can be specified with the monitor definition.
Right clicking on any monitor node will pop up a menu that allows you to enable/disable the monitor or delete it altogether. Keep in mind, if you assign the monitor to a variable that you maintain, for example in a Python script, this monitor will not be removed until you release this variable.
You can select multiple monitors and invoke the operation on all the selected monitors at once.