TrevD
As has been explained V6.181 is way out of date and you may care to update it.
I can only assume that you want to keep 6.181 for some "academic" reason since it will not respond to or work with any of the latest definition files.
But bear with me ... The Ad-Aware prog. does indeed "keep a copy" of the previous definition file when it installs the new one - this was (is) done purely in case there was an inadvertent problem with the new definition file.
Waaaaaaaaaay back when 6.181 was current, definition files were called "reference" files - they are now called definition files.
The current version(s) of Ad-Aware keeps the old file as "defs.ref.old" and calls the latest D/L'd file just "defs.ref".
Similarly the old 6.181 would have called the old reference file refile.old (or something similar - so long ago I can't remember exactly) and to re-use the old reference file you would have to locate it and rename it as just refile by removing the ".old" - but in order to do that you first have to delete (or preferably rename the current refile to some other name) obviously they cant both be the same name.
If, however, you are talking about nasties that Ad-Aware has Quarantined and you want to restore
those files back - you need to click the quarantine list select the items you want to restore (some, or all) and then click restore.
Hope the above may help.
But as stated - it is a bit of a mystery why you would want that old ver. that is no longer supported and will not recognise any new "definitions" .... It is worse than useless because it may give you a false sense of security when using it.
Cheers, Totro