Yeh i thought mine was glued as well but it turned out that it wasnt...after gettin a few cuts on my hands(no blood just skin) i managed to get it off using a foam mouse pad (that ive just replaced along with a new A4tech X7 mouse as my 7yr+ mouse finally died on me this week)
lucky me, mine came with no glue at all. It unscrewed with no effort at all. I find the lens to be pretty nice as is. Very clear with anti-reflective coating. What are you changing it to?