I have a old £50 note and I need someone to accept this from me?

If you're in the UK anyone will accept it, if you're in any other country take it to a money exchange office and they'll change it into the currency of your choice. Unless the 50 pound note is over 50 years old it is still legal currency and if it is over 50 years old it is worth more than it's face value and you can still exchange it but at a bank.