My dyed color is redish-brown I want to lighten it to a medium to dark blonde, what hair color do I use ?

Do you have red pigment? What is your natural hair color? How long ago did you color it? (Wondering if it's not too late to take the color out or undo without damaging your hair.) And last but not least, was this permanent hair color you last used or did you happen to use a temporary rinse? (Some last a month and some last a couple of weeks.) Need to know these things so that your hair doesn't come out purple and you also don't want to damage your hair.
Until you answer the other questions, if you used a permanent, you want to wash your hair a lot with a shampoo that has a lot of detergent in it. You might want to buy some hot oil treatment(s) as well because the washing to get the color out will cause your hair to become very dry and brittle.

If you wish to go lighter, you need to remove the artificial color in your hair first. Hair coloring will not lighten artificial pigment. ColorFix, ColorOops, Color Zap, and Igora Phantom are some of the best color removers. After that, most brand-name hair dyes may work.

Caveat: There's a lot more to dyeing hair than simply throwing a dye on the hair and letting it process. It's very often not possible to lighten hair as much as one would like -- at least not with a single-process haircoloring. There are definite limits to how light you can go. If you wish to go lighter than the limits (or less brassy), you have to bleach the hair and then tone it (double-processing).

Your dyed color is reddish brown, but you said nothing about your natural color. That's more important than your dyed color in deciding whether you'll have to bleach your hair or not.

These are reasons people go to salons -- so they don't have to worry about all of the variables. Some colorists are very good at what they do.