How can I delete all partitions on my MacBook Pro?

It sounds like you want to erase your computer's hard drive. To do that, open the Disk Utility app and you have the option to completely erase the disk. Be sure to select the upper icon to do a complete erase. Then you will have to reinstall a new operating system. Restart by holding down the Command + R keys at startup. This will enable you to use the Recovery mode to select a OS to download. Two more comments. (1) Be sure to back up your data before erasing the HD. (2) When downloading these very large files you should use a wired Ethernet connection and not Wi-Fi. Wi-Fi is too slow and corruption of the file will often occur.