The number of SSL connections is the maximum number of clients that can connect to the VPC in the same time.
Follow these steps to modify the number of SSL connections:
Log on to the VPC console.
In the left-side navigation pane, click VPN > VPN Gateways.
Select the region of the target VPN Gateway.
Click Modify Configuration in the Concurrent SSL Connections column of the target VPN Gateway.
On the purchase page, select a new number of SSL connections and complete the payment process.