Yes. You can upgrade to a higher plan at any time on the Settings → Plans and Billing page or the Pricing → Payment page to get more Credits, which will take effect immediately.
You only need to pay the price difference to upgrade your monthly plan.
Pro users can choose from three credit tiers: 100, 250, or 350 credits per month.
Max users can choose from multiple credit tiers ranging from 500 to 10,000 credits per month, depending on their usage needs.