Open the Preferences window though the main menu, then navigate to the Shortcut keys tab.
There are a number of actions that can be performed through keyboard shortcuts, these include: accepting and declining a call, muting and unmuting, turning speaker on or off and launching the SIP Accounts window.
Clicking the Edit button on a particular shortcut key opens the Edit Shortcut Key window, which allows the combination for a shortcut to be changed.
Please note that some combinations are existing Windows system commands so if set will not work.
These include: combinations consisting of a single key, combinations with Ctrl + Letter or Number, combinations with Shift + Letter or Number.