Update your existing browser first
Having an old version does not necessarily mean you need to switch to another browser (provider). In most cases, it is enough to update the old program and then restart it.
Chrome, Firefox and Edge have an information or checking page in the browser menu for this purpose. Opening it immediately starts an automatic search for updates and installs them. Safari, on the other hand, is updated together with macOS, iOS or iPadOS.
When no update is offered
On older operating systems, a current browser version may no longer be supported. For example, Firefox may refuse to update on Windows 7. The first step should then be to check whether a system update is still available for the device. PCs and laptops running Windows 10 or older should urgently be upgraded for security reasons alone, as these systems no longer receive updates.
If the operating system can no longer be updated either (Windows 11 in particular has demanding hardware requirements), the only long-term option is to buy a new device. Or, where available, use another browser that still accepts or maintains the older system. Continuing to work indefinitely with an outdated version is not a good solution.