I am using

APP HOLD "foldername"

before doing the actual HOLD so that I can reuse the report output...

does anyone know how to delete the temp files created by these HOLD?

You can use:
APP DELETEF appname filename filetype
command.
The syntax is described here:
IBI Support Link

You can use the operating system command, as well:
! operating_system_delete_command path_to_the_file(s)

One of the tricks I use is to put the HOLD files into the same directory that WebFOCUS uses as it's temporary directory CGI_TEMP_DIR(C:\ibi\WebFOCUS52\temp). I use this directory because WebFOCUS automatically cleans up temporary files after a certain time frame. The time frame is controlled by the _TempFileTimeout settings in the cgivars.wfs config file. This works great as long as all your pieces of WebFOCUS are installed on the same box (Client and Server pieces). What you do is MAP your HOLD directory to this directory using the APP MAP command. Give it a try.

Thank you guys...

this issue was just a part of a bigger problem...
and... it seems to become a hot topic.

Please refer to "sorting the report by any column" to see my concerns.