You need to complete a CREST transfer form and send this and the certificate off to the relevant registrar. (See web site of company shares are in to see who this is.)
When your wife disposes of the shares, CGT will be levied against her as if she had owned the shares from the original acquisition date at the original cost.
I guess you know all about your CGT allowances, and the 18% band before you hit the main 28% taxation level, but ask away if not. Also note that if the shares are approved options you can (with 90 days of issue) use them to feed your ISA and there is no CGT!
Ian