The flash programming utility, which is invoked automatically when you launch a debug session, can also be accessed at other times within the LPCXpresso IDE environment by clicking on the "Program Flash" icon on the toolbar at the top of the IDE window....
Note: the exact location of the icon on the toolbar may depend upon which perspective you have active.
Before clicking on the "Program Flash" icon, ensure that you have a project selected in the Project Explorer pane which is configured for the target that you are going to program. This will ensure that appropriate configuration options for the flash programmer are set.
Alternatively, if you select a .bin or .axf file within a project, the flash programming tool will also pick up the filename too.
Within the flash programming tool, you can then choose to program an image into the flash...
or by selecting the other tab, you can choose to erase the flash....
Generally it is also a good idea to ensure that the "Display progress log" option is enabled before programming/erasing. This will cause details of the operation to be displayed once programming completes - as below.