Product review (5 stars): pretty easy. Pretty much twist and pop out the ...
Being the logical being I am, I filled the inside with water first. Took a while since it had to settle down to the bottom of the stuff it was packed with to filter the water. Once I had it full, I replaced the old one from our refrigerator, pretty easy. Pretty much twist and pop out the old one then push in the new one and twist in.
Tried the water dispenser, got the extra water out, then it made the kind of noise you hear when a machine is trying to siphon the water out and getting nothing (about two seconds), and finally the water came out. Just to be sure I filled a glass full and threw it out. Filled another glass and drank it, and it tastes much better, cleaner... before it had this weird very slightly moldy taste (I dunno, I must be really sensitive). Anyway, it works just fine.