Changing strings and figuring out which octave is which can be confusing when you're just beginning the harp. Check out these videos below to help you get more comfortable changing strings.
How to tell which octave string you need:
https://www.youtube.com/watch?v=ACctcdAXX_0#t=116
(You can skip 2:18 to 4:14 because it doesn't apply to Lyon and Healy, Camac, or Salvi lever harps. Also, the top two strings on a concert grand harp are called 00 F and 00 G or the zero octave)
How to tie a knot on strings in the upper octaves:
How to tie a know on strings in the mid-range octaves:
How to lock a string on the tuning pin:
How to change bass wires:
https://www.youtube.com/watch?v=aXHU7gHdscE