To fix / repair / install new lock for Balcony sliding door

Total Door sixe : 2, 8 meter wide x 2, 0 meter height (out of 2, 8 meter wide - 1, 40 meter is fix and 1, 4 meter is sliding door) Original Door supplied : Knut stein trevarefabrikk, Stokke in year 1984 (i think) Door is in excellent condition and very solid : ) but very recently we had problems with the Lock handles, which is getting stuck sometimes when we are trying take up the handle to lock the door.