League of Legends reinstall problem

After reinstalling windows I have been having problems reinstalling league

1. The download size is 4gb for some reason
2. Every time the client exits it doesn't save the progress and restarts the 4gb download
3. When the download reaches around 80% it says an unknown error has occured

I've tried unintalling and installing multiple times but it doesn't work Plez help*[sg-janna]*