An Internet Service Provider (ISP) is the company from which you purchase internet access services (like AOL or IServ). A browser is a piece of software on your PC which allows you to access things like web sites, Internet access. Examples are Microsoft Internet Explorer or Mozilla Firefox. Upgrading your browser is important. It insures you have the most current version with the most up-to-date features, speed and options.
But in most cases what is needed the most is to upgrade the encryption level (sometimes called cipher strength) to 128-bit encryption. This is for security and privacy, and is a requirement to used by online banking. Depending on the browser, you can sometimes upgrade encryption level by itself, without any other changes to the browser. Visit the web site for your browser manufacturer (for example, Microsoft or Firefox) and you will find instructions for encryption levels.
NOTE:  AOL has its own proprietary browser that you receive when you use AOL as your ISP. AOL users  may not have to worry about encryption levels if they upgrade their AOL software.