I have a Netgear router that is compatible to flash DD-WRT. I have read you can use mac windows or linux. I only have a RPi3 no other computers. Will my Rpi3 work for this? I am running the latest Rasbian and have a 16G sd card.
Since you don't specify the router, I'll give you the generic answer:
Assuming you're running a mainstream distribution (like Raspbian), a RasPi is for all intents and purposes a Linux PC (just running on an ARM chip instead of, say, an Intel one).
DD-WRT's methods of upgrade in general (web browser, TFTP) will work fine on a RasPi. Unless your router has a really weird binary-only client of some sort (that happens to be available for Win/Mac/Lin), you'll be fine.
I don't have any experience with Win 10 on a RasPi 3, but I imagine this will hold true here as well.
You can do this from any OS, you need just a file upload compatible browser (all existing browsers). Connect to your router (wi-fi, lan), open web browser, type IP address of your router, login, go to the menu with firmware update interface, select DD-WRT firmware file and press upload button.