There are several reliable tools you can use to download the latest firmware for the Samsung SM-G900A smartphone directly from Samsung’s servers.
When you visit websites to download Samsung firmware files, you have no way of verifying whether or not the files did in fact come from Samsung’s servers. Therefore, even though it’s a bit more work, you are better off using one of the free firmware downloading tools that are known to download the firmware files directly from Samsung’s servers yourself. Once you have downloaded the firmware, you can flash it with the Odin flashing tool.
There are several reliable tools you can use to download Samsung firmware for free; however, there is no de facto tool. All of them are very similar, but there is no way of reliably knowing which one is best for your smartphone until you try using them. They each will attempt to download the latest firmware directly from Samsung’s servers.
SamFirm_Reborn is one of the most commonly used forks for the original SamFirm tool. It’s by no means the only fork though, so we will mention the other good ones next. SamFirm_Reborn is often used more than the others because of the name but it is not necessarily more reliable. That said, this tool does always keep up with Samsung’s server-side changes, which makes it very reliable.
Another fork of SamFirm is the SamFWTool. You may prefer using SamFWTool thanks to its automatic detection feature that will automatically detect what smartphone it is you have. This saves you the hassle of trying to enter the details manually which can be troublesome for some.
Another fork of SamFirm is Frija. Like SamFWTool, Frija comes with automatic detection for detecting your device’s model number and will then try to download the firmware files for you. To use it, connect to the desktop in MTP Mode and click on the Auto Detect button and then the tool will download the latest firmware.