If you are looking for the Realtek PCIe GBE network card driver then you can look for the driver below. The hardware in the Inspiron 3138 is the same hardware which you will find in the Vostro 5470 as well as in the Vostro 5480 and the Inspiron 3043 computer. There are other software such as that for the USB driver and the UART drivers for additional equipment which many be connected to the computer. Note that this is a Windows 10 both 32bit as well as the 64bit driver.
Inspiron 3138 : Realtek Network Driver
You will need to download the Realtek network card for the Inspiron 3138. Download the zip file and open it when you are finished downloading the file. Open the file and click on the file to install the driver. It may install or it may also extract the drivers into the Dell directory on your C:\ drive. Open the directory and click on the install file in the directory which the software created. This take a few seconds depending on your computer hardware.