To use these D'Addario EXL158 strings, first make sure your guitar is in a stable position. Loosen the old strings one by one and remove them. Then, start threading the new strings through the bridge and the tuning pegs, starting from the lowest string. Tune each string slowly to the desired pitch. As for maintenance, wipe the strings with a clean cloth after each use to remove sweat and dirt. Also, avoid leaving the guitar in extreme temperature or humidity conditions. This will help keep the strings in good condition and ensure they last longer.