You can withdraw your money from bookmakers and exchanges at any time.
Each bookmaker or exchange you use will have a "My Account" section, or similar, where you will have the option to withdraw your money.
Below you will find some examples.
Withdrawing from Betfred
Click this blue box in the top right of your screen
Then click withdraw on the dropdown menu
Withdrawing from Betfair
Click on my account in the top right corner of your screen
Then click mon y Betfair account
Then click withdraw funds on the right side of your screen