Read or write a file backwards

Hello everyone.
I saved a “u” file where u is the solution of an evolution equation in the form: x.y.u(x,y) at each iteration of time t of t=0, x.y.u(x,y)… at t=1, x.y.u(x,y). I would like to know how to create another file whose elements are: t=1, x.y.u(x,y)… to t=0, x.y.u(x,y). That is to reverse the order of the elements of “u”.