One is to make parameters 3 and 4 dependent on parameter 2. It's a lot to describe in detail here, but you could start with a search on dependent parameters (dependent is the key word here) and we can discuss the details more here if you like. They can be a little tricky the first time you do it, but it is possible to do exactly what you are describing.
There is a second way that I often use when I want the users to know other parameters exist but they are only allowed to actually enter them when its appropriate. That is to set the LOV on parameters 3 and 4 so that the default and only value is "NA" if parameter 2 is the one that doesn't use parameters 3 and 4. When parameter 2 does require parameters 3 and 4, then the list of values includes whatever is appropriate. This can be done by use of a Table type value set for parameters 3 and 4, with the where clause of the value set incorporating parameter2 to change the list of possible values.
Hope this helps. Giving a quick answer here, I can provide more detail if you'd like.