Insert the memory card into your computer, and open the computer file browser. It should be listed in the main view where it shows your hard drive and disc drive. Left click on it once to highlight it, then right click and select properties. In the box that appears, under the general tab, there should be a heading that reads "attributes." Just under that heading you will see "read only," uncheck that box.
Now exit the properties window and right click on the memory card again. Select format. In the box that appears, click restore device defaults, and then check "quick format." Hit apply.
Also some flash drives have a small switch on the side that acts as a write lock. If the process above doesn't work, check if there's a switch on the flash drive and try flicking it over then re-applying the steps above.