It depends on what cache you are talking about. There are processor
caches, and the system's cache of files read from/written to disk. (Leave
all these alone).
Then any browser has its own cache of files downloaded from the net
(Temporary Internet Files in the case of IE - you clear that and the
cache of sites recently visited at Internet Options using the buttons on
the General page) - you clear those of other browsers in their menu
systems.
And individual programs cache data for their own purposes; often in the
Temp folder under Documents and settings\you\. . .
Cleaning temp cache as well as a registry cleaner can be found in this free program:
http://www.ccleaner.com/
To manually edit the registry go to
start/run/ regedit
You can search the registry from the
Edit tab then
Find.
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Altering system files; & or modifying the registry can be risky and D-A-L.com and its members cannot accept liability for any adverse effects caused by following advice freely given on this site.