The Realtek network card river in the Inspiron 5439 has a Windows 10 driver listed below with both the 32bit as well as the 64bit driver in the same file. The network card is also used on the Vostro 5470 as well as on the Vostro 5480 which are all from Dell. You will need to download the zip file which is attached below. Inside the zip file you will find the Dell driver file which will install or extract onto your C:\ drive. Note that this driver was the last driver which was released in October 2015.
Inspiron 5439 : Realtek GBE PCI Network Driver
The network driver is listed below for download in a zip file. download the file and open the zip file once downloaded. Now click on the file inside. The software will either install or extract to your main hard driver, normally the C:\ drive. If it extracts then you need to check on the main drive as it will create a Dell directory. Open this directory and then click on the install button and the driver will install on your computer. This was the last driver released in Oct 2015 and it is known as version 10.1.505.2015.
Supported Operating Systems : Windows 10, 32-bit / Windows 10, 64-bit