Right now, the max CPU is limited to 4 CPU cores.
If you have reached the CPU limit, no further upgrades are available, then it may be time for a VPS or Full Dedicated Server.
The number of CPU cores you are using will probably not represent the number of CPU cores you will need in a VPS or Dedicated Server.
mySQL, backups, stats processing, mail servers, etc are not included in your CPU usage. †So, if you are maxed out at 2 CPU cores, you may need 4 CPU cores on a VPS or Dedicated. †If you are using 3 CPU cores, you may need more.
Minimum Ram should be 2 gigs with a recommended 4 gigs on a dedicated server.
A VPS can be upgraded on the fly from 1-16 cores or 1-16 gigs of Ram. †Dedicated server CPU's aren't always upgradable, RAM is usually upgradable by taking the server offline and adding more.
Please open up a support ticket for a quote on either a VPS or Dedicated server for the best possible deal.