(NH4)(4)H-2(SeO4)(3) single crystals undergo a transition to superionic phase at T-s = 378 K and the phase is characterized by high structural disorder. When the crystal is cooled from highly disordered superprotonic phase to T much less than T-s the order, characteristic of low-temperature phase (trimers formed by three SeO4 tetrahedra linked with two short hydrogen bonds, lying along [0 (2) over bar 1] direction), has to be recovered. The recovery process, termed by us as structural relaxation, was studied by means of impedance and Raman spectroscopy. Results of conductivity recovery measurements allow to distinguish three rates of conductivity decrease. Time variation of SeO4 skeletal modes after cooling the crystal from the superprotonic state to temperatures T much less than T-s points to the following processes of the recovery: i) relaxation to the low-temperature molecular structure (formation of trimers is proceeded by formation and disappearance of dimers as a transitional form) and ii) relaxation to the low-temperature crystallographic structure (trimers lying along [0 (2) over bar 1] direction). We observe the process of dimer formation and disappearance within similar to 30 min at 303 K, whereas the formation of trimers lasts similar to 1 h at the same temperature.