According to Dell, the following WiFi modules were available at the time for that Dell Laptop.
Dell Wireless 1390 (802.11g), Dell Wireless 1490 (802.11a/g), Dell Wireless 1505 (802.11a/g/n)
The 1390 is limited to 54Mps.
You can get after-market wireless cards, but you'll need to check if it's two or three antenna wires. It may or may not work, but you can get an 802.11ac card fairly cheap on Amazon.com or whatnot. The easiest option is just to get an 802.11ac USB dongle; install drivers and plug it in. In addition, you're router that supplies WiFi will need to be in the 5Ghz band to reach higher speeds.