Note that R and RStudio are different. Differentiating R from RStudio, (think of R are the engine, RStudio the car, and you the driver.)
So when you install RStudio you'll need R to be installed to make use of the IDE.
I don't have experience with Anaconda's RStudio install, but to uninstall that in Windows I think you'd go to window's "add and remove programs" tool.
Also, welcome to community.rstudio.com!