Within each LPCXpresso project, there will be a "launch configuration file" for each build variant, which is used to store the settings for a debug connection for that build configuration. These will be created in the root directory of a project the first time that you launch a debug session for that project and are typically called "<projname> Debug.launch" and "<projname> Release.launch".
Normally, there is no need to touch the launch configurations, as the default settings created by the tools will be suitable.
However in some circumstances, you may need to modify them - typically under direction from an FAQ. In such cases, the best way to do this is via the "Launch Configurations" entry on the context sensitive menu available from the Project Explorer view...
A number of options are available here:
WARNING - Modifying the default settings for a launch configuration can prevent a successful debug connection from being made. Make changes with care!
After selecting the "Edit current" or "Create and Open New" launch configuration menu entry, you will then see a new dialog box pop up, which looks like the following...
Most settings that you may need to modify can be found in the Debugger tab, in the Target configuration sub-tab (as shown in the above screenshot).
Some examples of modifications that you may need to make in particular circumstances are :