The law will vary from one country to another. Since we don't know where you are it's difficult to answer.
Normally, if your father left a will there will be no difficulty once it has gone through probate.
If he left no will you should talk to the manager of the bank branch you deal with and ask him what you have to do to access the account. He will be able to tell you what steps you need to take. After that, and depending on what he says, you might need to hire a lawyer.
