Basically the forum is a great start to learn the platform, the Guide section is also very helpful.
Back to your request
To summarize what‘s possible at the moment:
this is possible on the calendar view → Options → Delete (Trash Bin) Plan
You can do that by changing the start date of the plan and reapply
This is not possible at the moment
When you update the plan, you can reapply the changes, and they will appear in the calendar. If you update a workout in the library that was used in a plan, that workout will not be updated, since it always exists in the plan as a copy of the workout.