Edit DRC using DRC window - Allegro PCB Design L (legacy)

Hi, 

I'm trying edit DRC's using DRC window, but the values are "read-only". How to solve this problem?

I'm using  Allegro PCB Design L (legacy) with Linux-x86(CentOs) and I want to change the current value for a constraint value required in my project (using .brd extension).

Thank for your support,