CLEAR CHAT FROM MEMORY WHILE IN CHAT

I’M LOOKING FOR A PROGRAM THAT WILL CLEAR MY MEMORY OF THE CHAT THAT IS STORED IN MY COMPUTER WHILE I AM ONLINE AND CHATTING.
WINDOWS LOCKES UP AFTER MY MEMORY GETS FULL.
I NEED A PROGRAM THAT WILL DELEATE THE OLDER CHAT IN MY MEMORY WHEN IT GETSTO THAT POINT.