inspiron 15 3520, windows 10 compatibility?

Hi!

I think that GWX ("Get Windows 10") application made a wrong prediction in your case, since both WLAN adapters that come with Inspiron 3520 series laptops are supported by built-in drivers in Windows 10. Same goes to the Fast Ethernet controller that you have.

I understand that you can't afford taking any risks, so here's what I would recommend you to do.

1. Detect the kind of WLAN adapter that you currently have. To do so, press Win + S on your keyboard and type in "Device Manager", which will allow you to launch the eponymous tool. Locate the "Network adapters" entry, expand it and see what you got. If there's a line that says "Dell Wireless 1506", then you need to download this package, exclusive to Windows 10:

downloads.dell.com/.../Network_Driver_X8VN6_WN32_10.0.0.318_A00.EXE

In case you've got "Dell Wireless 1704", you should download this one instead:

downloads.dell.com/.../Network_Driver_P9WVJ_WN32_7.35.267.0_A00.EXE

These work with both 32- and 64-bit Windows 10 editions, but not with any previous version (like Windows 7 or 8.1).

2. When you're done with your Windows 10 installation tomorrow, simply run the package you've downloaded and follow the required steps. You're all set!

Note: it's fine if you just download both *.exe files and run them in sequence from within Windows 10; the one that's incompatible will inform you without performing any kind of installation and/or affecting your PC in any way.

Good luck!