Yes, you can purchase additional vCPU, RAM, disk space, Bandwidth resources during the VPS signup or later on when you need them.
Order add-ons from member’s portal area
It is the most convenient way to buy add-ons. All you need to do is log in to the client area, select the VPS service and purchase the additional resource for it.
Please refer article
https://help.softsyshosting.com/en/knowledgebase/article/windows-vps-plan-changes