The replacement will be an insert. You will need to remove the top nut that holds the spring 'hat' in place (connects to the threaded section of the strut shaft). (use a spring compressor).
Then, to remove the old insert, you will need to remove the gland nut. Sometimes they are a PITA, sometimes not. I haven't had the problem yet...just used a plumbing wrench on the hex.
Tim