The circled areas on the image indicate the switches and their respective connections that will need to be desoldered and replaced.

If you don't have access to a desoldering gun, this will be much easier by cutting the old switches into pieces. Take care to leave as much of each of the pins as possible to provide something to pull against for removal.

The switches are shaped so they must be pressed into the socket with a decent amount of force; this is what makes the removal so difficult.