Short answer
Open a ticket with Sales naming your storage service and the size you want from the storage plans. Your files stay where they are.
Sizes
Storage comes in 2 GB (free), 100 GB, 250 GB, 500 GB and 1000 GB, paid monthly or for 3, 6 or 12 months at a time. See storage plans for prices.
Need more than 1000 GB?
A managed Nextcloud server gives you far more space and your own users. Ask Sales for a quote.
Questions people also ask
Can I move to a smaller plan?
Yes, at your next renewal, as long as your files fit in the smaller plan. Ask Sales in a ticket.