access denied when changing controller properties

I need to change the values of controller properties as I am getting Connection Timeout: waiting time when establishing a connection

Need to perform the below activities but it is not saving the file and saying access denied,

Error Code: NL-NETWORK-01 Message: Network error: An IO error occurred sending the request. Details: java.util.concurrent.TimeoutException: Idle timeout 300000ms
These settings may be edited in the <NeoLoad>/conf/Controller.properties, file in the Runtime section.
You simply need to change the values for the runtime.connection.timeout and runtime.so.timeout keys. The values are expressed in milliseconds (for example, 30000 for 30 sec.). Settings these key values to 0 will create infinite timeouts (default behavior if no values inserted).