"Sending a signal" is a UNIX thing, and it requires you to use the Terminal. First, type ps ax to list all the processes and numbers. The numbers are the first digits in each line of results, and they're important for the next step. Find the pppd process, and then issue a kill command: kill -HUP 1234, where 1234 is replaced by the id for pppd process you found in the previous step.

