remove default programs from recomended program list

Hi Guy's,

Whilst on holiday my son has placed Adobe reader and Notepad into the
recomended program list and made them the default programs for my wifes
Kareoke files.
I have added the correct program into the default list but once i turn the
computer off and restart at a later date it returns back to using Adobe.
The only solution i can think of is to remove Adobe and Note Pad from the
DEFAULT PROGRAM list and them back into OTHER PROGRAM list and then place the
correct program back in as the default.
Can any body explain to me how this is possible as the only information i
can find is how to change a default programe but it does'nt remove any others.
Thankyou for listening.