You can increase your Google Drive storage incrementally from the free 15GB up to 30TB for a monthly charge.
To purchase the storage upgrade, go to www.google.com/settings/storage (sign in with your Google account if needed). Choose a plan you want to upgrade to and follow on screen instructions to purchase it.
Here's the monthly price for the upgrade:
15 GB for free
100 GB for $1.99
1 TB for $9.99
10 TB for $99.99
20 TB for $199.99
30 TB for $299.99