my beko wma1512w washing machine wont spin?

my washer at the moment will not rotate on a wash or spin the belt keeps slipping off although it is not stretched i have researched and it could be due to the pulley , how do i adjust it ? the drum also wobbles dramatically but this could also mean that the pulley pin or bolt or bearings are shot can anyone give advice on how to go about firstly altering the pulley ie tightening