Hi clubNW1414, I am also taking the June LSAT! I did not use the temporary login, as I had already attached my LSAC account to ProctorU, but I would use it if I were you so that your exact test registration number translates over. Best of luck!
I used the temporary log in first, then from there I was able to edit my details under account settings to change my password etc. You should be able to select your account details on ProctorU and make account changes!