amCharts employee here. The branding text/logo is on the free version of the library. As stated on the license terms:
Free license
Use anywhere you want as long as you don't mind a small amCharts attribution on charts
If you want to remove the text, you have to purchase a license. See the license FAQ for information on what license is appropriate for your use case. You can reach out to AmCharts support for further clarification on the license terms.
If you already have a license and are using amCharts v3, just download the files from the support site, upload them to your web server and use those instead of the files on the amCharts CDN. If you're using npm or just wish to use the CDN files with your license, contact amCharts for instructions on how to apply your license. Do note that support for amCharts v3 will end at the end of 2020, so you may want to consider migrating to v4 for any further support and fixes.
If you have a license and you are using amCharts v4, the instructions are available in your support account. You will need to create a support account if you don't already have one and attach your license (order ID and email used to purchase the license) to your account to view the instructions.
Finally, if you're still having trouble with applying your license, contact amCharts and provide your order details.
We don't provide instructions on how to hide credits on a public forum for obvious reasons.