I have replaced the slide seals on my bedroom slide and the vertical seals on my living room slide. Once you have the replacement seals and a ladder it is not very difficult.
1. Take the metal L trim off that covers the seal and remove the old seal.
2. Be sure the slide is not fully extended, move it back in about 6 inches.
3. Cut the new seal about 6 inches longer than the old seal.
4. Spray Windex on the seals T edge base and slide it into the track, starting at the top and working down, being sure the inner lip is in the track from top to bottom.
5. Cut the bottom edge of the seal to fit as necessary.
6. Replace the metal L trim.
7. Use black silicone caulk on any gaps or holes.
Here is a link to more info:
Need new seals on bedroom slide