If you search the forum using the above heading you should find a series of responses to the same question from August 24th last year - on page 4 at present.
I have done mine twice in 11 years, bit fiddly but no problem. I thing it works out at about £35-£40 to do all five seals.
I had trouble finding the seals the second time but found dive shops sell them - check out internet shops (there are a couple of sizes so you need to choose based on your existing ones and you will need to cut the neck around one of a series of rings to get it so it goes over your head but still seals at the neck comfortably
Now is the time to do it!!!
Best wishes
Steve