For this you need to start a new season, before you start your season go down to the 
menu that says ManageTeams>Transfers>club transfers. When it says select team pick any 
team that you want a player from look on their team click A and you can transfer it to 
any club in the world say if you wanted to transfer Messi to liverpool you would go to 
barcelona and select messi click a go to country england leauge Epl Team Liverpool and 
click A you can do this for any players , next you make a new season as say liverpool 
then you will have Messi in you squad.
Warning: If you are already in a season it will not work, you have to start a new season 
ty Comment on this please , at max7.90@hotmail.co.uk