how can i change the lim X-->4 insted of x-->0

If you have lim(x→4) for some function, f(x)

and you want to change the limit to x→0, change the function  from f(x) to f(x-4) 

As an example:  lim(x→4) x² - 8   would change to:  lim(x→0) (x-4)² - 8