The difference between 'if' and 'whether' is that 'if' introduces one condition and 'whether' introduces alternative possibilities usually with 'or not' implied or expressed. 'She asked me if I loved her' 'She asked me whether I loved (or not)' 'If' we save carefully for the next year, we can afford to spend next summer travelling around Europe. 'Whether' we manage to save enough money or not, we're going to spend next summer travelling around Europe

In colloquial English (and most written) they are interchangeable. Either is acceptable, with "if" being more modern and informal. "Whether" is not too formal though.

They both mean the same.