The proper way to fully uninstall conda (Anaconda / Miniconda):

Remove all conda-related files and directories using the Anaconda-Clean package
conda activate your_conda_env_name
conda install anaconda-clean
anaconda-clean # add `--yes` to avoid being prompted to delete each one


Remove your entire conda directory
rm -rf ~/miniconda3


Remove the line which adds the conda path to the PATH environment variable
vi ~/.bashrc
# -> Search for conda and delete the lines containing it
# -> If you're not sure if the line belongs to conda, comment it instead of deleting it just to be safe
source ~/.bashrc


Remove the backup folder created by the the Anaconda-Clean package
NOTE: Think twice before doing this, because after that you won't be able to restore anything from your old conda installation!
rm -rf ~/.anaconda_backup