Rtools already installed, but package prompts to new install then quits because Rtooll is already installed

Question

I tried to make the title as descriptive as possible. I`m trying to install the package Giotto on Rstudio, with

library(devtools)
library(remotes)
remotes::install_github("RubD/Giotto")

Then I get a prompt saying

Building R package from source requires installation of additional build tools

When clicking "yes" it starts downloading Rtools35. After the download is finished, another prompt gives

Another version of Rtools is already installed in: C:\RBuildTools\3.5. It is recommended to uninstall the old version before installing the new version. Do you want to proceed anyway?

Both "Yes" and "No" fail to install. I also checked

> pkgbuild::rtools_path()
[1] "C:/RBuildTools/3.5/bin"

I tried uninstalling Rtools, but I don't have the privilege. Is this the only solution?

Thanks!