A method for updating firmware in a user terminal comprises dividing files with modified contents into a plurality of groups and assigning each file with respective offset. The method then performs bitwise XOR operations between the plurality of groups onto the backup buffer. Consequently, the method stores a result of the bit XOR operations on the backup buffer into a non-volatile storage as a backup file. An apparatus for updating firmware comprises a processing circuit configured to divide files with modified contents into a plurality of groups and assign each file with respective offset. The processing circuit performs bitwise XOR operations between the plurality of groups onto the backup buffer and store a result of the bit XOR operations on the backup buffer into a non-volatile storage as a backup file.