If you go to
http://h17007.www1.hp.com/us/en/enterprise/servers/products/service_pack/spp/index.aspx
and select OS supplementals you will find the 2012R2 bits, if needed, but i think your server is too old and not supported by hp for 2012, hence you will probably get a problem with drivers.
Quickspecs:
http://h18004.www1.hp.com/products/quickspecs/productbulletin.html#spectype=worldwide&type=html&docid=12199
OS support: Windows 2003
see also
http://h18004.www1.hp.com/products/servers/windows/index.html
