Generalised Linear Modelling to analyse the customer retention characteristics of the mortgage portfolio

Given data/variables on mortgage holders at a specific bank, i.e(salary, postcode, account number, loan amount etc), how can I use GLM to decide how different customer circumstances affect whether to choose to remortgage at the same bank they took their original mortgage at or whether they choose to remortgage at a different bank. I am trying to identify the factors driving customer retention.