The incoming directors into the company will need to fill in a B2 for the new registered office and a B10 appointing the new Directors/Secretary to the Company.
The outgoing Directors and Secretary should tender their resignation in writing also, which should be given as part of the pack to the purchaser. The B2 and B10 are what needs to be lodged with CRO.
As regards share transfers, these are not dealt with at CRO and there is no point going there. The purchaser should make you fill out an indemnity form for lost share certificates. Given the time frame, and the value involved they may not do this. If you purchased your company from a formation agent, you may not have been issued with share certificates, as sometimes they do not come as part of the package.
If not, write up new ones. The share transfer forms, along with an SD4 form and a draft made payable for the stamp duty (1%) should be sent to the stamping branch in Dublin Castle.