Hi david..not sure what exact kernel you want other than pae...but I will give an example that works from command line (you can get in synaptic also)
first be sure you do an 'apt-get update' and you are connected to the internet.
I could explain all the options, kernels and such, but I am going to go the quickest path for this response. then you can always go from there - this will install the 3.13 pae kernel from backports which will match the non-pae version shipped.
enter the command
'sudo apt-get -t wheezy-backports install linux-image-3.13-0.bpo.1-686-pae'
once done, reboot and you will now have two kernels to choose from - the original non-pae and new pae
also once you run htop or whatever you want, you will see your multiple cpu's, etc. I would keep the non-pae kernel for a bit until you have tested and are comfortable all things are working as you expect.
Command line, or synaptic or update manager?
If via synaptic or update manager, there is a known installer bug/issue thats stickied at the top of the R8 forum.
enter the command 'gksu-properties' and change to menu value in popup to sudo (its probably set to su) - this fixes the password bug with update manager and synaptic.