Tracy,
The schedules can be removed, but the warning about assignments tied to the schedule indicates that you have Participant and/or Staffing Assignments that are tied to those schedules. You may want to run some reports to figure out who is tied to those old schedules and should be updated or have their assignment removed. Be sure to include inactive Staffing Assignments as well as active assignments because you could easily miss those.
Once you have figured out who is still tied to those schedules, you can figure out what the best move will be. If you have a lot of assignments tied to these schedules, you can open a support ticket to ask for some help in changing or remove them. If you have a smaller number, you can change them yourself and then delete the schedules. It's hard to say for sure without knowing who is still tied to those schedules.
Either way, you'll probably want to review the assignments before changing or removing them. That way you don't run into the possibility that you are affecting otherwise legitimate assignments just to correct a schedule issue.
I hope that helps you some.
For Him,
-Peter Schott