Hi Abhijeet,
After looking at the images I see that the subsystem is locked to modifications. This could have happened because the Read/Write permissions of the subsystem might be set to "ReadOnly". You can change the Read/Write permissions of the subsystem to "ReadWrite" by right clicking the subsystem, and then clicking the "Block Parameters(Subsystem)" button and then change the "Read/Write Permissions" dropbox under the "Main" tab.
To know more about setting these Read/Write permissions refer to the following documentation:
Hope this Helps!