Display/Delete Relations PropertyManager in creo?

It looks like you don't have any relations defined in this particular sketch.
Also, judging by the initial post and your explanation, there might be a slight misunderstanding: relations in Creo are mathematical equations defined to drive dimension/parameter values.
Relations dialog box won't show constraints like "Tangent", "Perpendicular" "Equal Length" and so on, all those constraints are displayed next to entity they govern and I'm not familiar with any "Summary" view for such attributes.
So, if you look for any additional, mathematical expressions used to refine behavior of certain dimensions/parameters, Relations are the place to go. If you'd like to see a list of all geometrical constraints (like Tangent, Equal, Parallel), there is no such summary available, just constraints icons for any given sketch entity.