Yes. For upgrades, you will be billed a prorated price that is for the remainder of your current billing cycle. For example, if you have a service that cost $10 per month, and you request an upgrade 15 days through a 30 day billing cycle, you would need to pay roughly $5 to complete the upgrade. For downgrades, if possible depending on the service, you will be credited the difference to your ExtraVM credit balance.
Open a support ticket requesting the upgrade. We will create an upgrade order that you must pay for, then you can reboot your VPS from our control panel for the new CPU and RAM allocation to take affect. If you wish to use additional SSD storage that comes with a higher plan, you must reply to your upgrade ticket requesting the drive space be increased manually on our end. Once it is done, you must reboot the VPS then use any common partitioning tool to resize the appropriate partition to use the extra space. Common tools are resize2fs (available on all Linux distributions), you can use a Linux rescue image, or you can mount the GParted ISO and boot into GParted to manage your VPS partitions and modify and extend them.
VPS cannot be downgraded.
You can request an upgrade or downgrade anytime via support. Some upgrades may require an IP and port change that you connect to your server with, however your server files will not be changed.
For Web Hosting:
You can request an upgrade or downgrade anytime via support. If downgrading, ensure your web hosting account fits within the resource allocations of the smaller plan before downgrading, otherwise your website may not load due to resource limits being hit.