Packages from the Start, Business, RS, categories can be upgraded with additional space but in general we recommend an uprade to the next hosting package in order to benefit from a full resource increase (cpu,ram,etc).
Reseller packages can also have additional IP's added to them.
For VPS packages all resources are available (cpu,ram,space,ip,etc)
In every case depending on your needs we can recommend an upgrade to the next hosting package.
In order to purchase additional resources you will have to contact the commercial department.