This article is from the Recreational Figure Skating FAQ, by Karen Bryden with numerous contributions by others.
You should periodically check the screws which hold the blades on,
especially when the skates are new and make sure they are tight. If a
screw is stripped or won't stay tight, water is probably getting
inside the screw hole and the leather of the sole itself causing the
hole(s) to expand and soften. What you should do is bring your skates
to a reputable skate shop and have them take the blades off, sand off
the top layer of enamel, re-plug the holes, and re-coat the soles
before putting the blades back on. They will put screws in new holes
wherever possible. If the soles are really rotted out, then your only
option other than replacement is to send them back to the manufacturer
to get new soles.
Repeated removal of the screws is undesirable. The threads in the
holes will strip after a few remove/mount cycles. Then you'll have to
use different holes, and if they're all stripped, you'll need to
repair the holes. Although it is best to leave this kind of
maintenance to the sharpener, you can plug the hole yourself in an
emergency: Take a piece of leather lace and cram it into the hole
together with lots of leather or hide glue. If you don't have any
leather laces, slice off a little piece of a wooden matchstick, put
the matchstick into the hole, and replace the screw.
If the the screw is really rusted or seems rounded off, get a new one.
You might have to drill or poke a starter hole for the new screw. In
this case it is better to let your skate shop can do the dirty job for