Can I change the Powered by text in my store footer?

It depends on your plan. Go to Settings → Web Settings → General Settings and scroll to Footer Branding:

• On a paid plan, enter your own Powered-by Text and Powered-by URL, then click Submit. The line stays visible but shows your wording and link.
• To hide the line entirely, white-label must be switched on for your store by the Wcart team. Then you can untick Show "Powered by" in the footer.
• If your plan is free, these fields are read-only.

The note under the fields tells you which applies to your store. The same line appears on printed invoices and email footers.