Live Agent - End User Inactivity Setting - where do I change the setting to extend the default set

[Nick124]

In live agent chat once a conversation has been initiated after a period of inactivity (150 seconds)  the end user gets he following message:
"The conversation is timing out, are you still there?"
if no further response ( a further 240 seconds)  the chat automatically ends . 

How do I change the setting so that these default settings are extended? We have employees who work on trade counters and often they will take longer than this period of time to pick the conversation up again.

Thanks.