You can delete all chats by by clicking on Tools > Options > IM settings > Clear history.
If you want to delete chats with one contact it's more complicated.
I just need to delete 1 contact chats, how do I go about it please? i don't want to delete all chat history
You can't do this using Skype but there is a 3rd party application, called SkypeX, which you can use to delete selected chat messages from your computer:
Actually, you can do the same using any Sqlite database editor (e.g. SQLite Database Browser; http:/sqlitebrowser.sourceforge.net), but this requires some knowledge of the SQL language commands.
In any case, note that the chat messages will only be deleted from your own computer and will still be readable on your contacts devices.
Procedure to delete a single contacts history from Skype (desktop)
1) go to http://www.sqlabs.com/sqlitemanager.php
download the exe and install (you can just use the demo version)
2) locate the main.db
win 7 the path is c:\users\USENAME\AppData\Roaming\Skype\SKYPE_USER
win xp should be in application data\Skype\SKYPE_USER
3) open the database
you cannot open the db with skype running
4) run the following query on the database
delete from messages
where dialog_partner like'%your_approx_want_to delete_username%'
the xxxx_username is the username you provided for the user,
and not the user itself (so what you see when it shows you someone logged in)
the manager itself is self explanatory on how to run a query
when i try to locate main.db-journal using SQLitemanager it's asking encryption key???. what whould be that key?
You should not try to opem main.db-journal but the main.db database file. Be aware that this file might just be shown as "main" but with description "Data base" or "DB file" in the Type column. the main.db-journal is only a temp file created when the main.db file is used.