Complex sentence: The main stand that has been there since the stadium was first built is a small two-tiered structure, dissused terraceing from the conversion to an all seater can still be seen towards the end of this stand.
Split into simpler sentences: The main stand that has been there since the stadium was first built, is a small two-tiered structure. Terracing disused since the conversion to an all-seater can still be seen towards the end of this stand.