Please help Blender subdivide problem

help i want to make a castel wall a realistic one for one of my projects but i have subdiveded the top of the meshes to make the wall kantels to make it like its a castle but when i want to subdived the fornt of the wall or ather parts to make it look realistic and not blocky i see now subdivd an i only se stips moving an my fps go,s lower so please help me whit this problem thanks in advance

Could you offer a screen with more info, what you try to archieve?