Win 10 how to boot and select the boot system?

Set the first method of selecting startup: right-click my computer-> Attribute-> Advanced system settings-> Advanced-> Startup and fault recovery->; Settings-> Select the system that needs direct access, set the following time to 0, and restart the computer to complete;

Method 2: If you decide to use win 10 without rolling back to the previous version, you can set it as follows:

1. Enter msconfig for operation, as shown in the following figure:

2. Open tab-Boot； in the pop-up management interface;

3. Here you can see two startup items, which set the system to keep the default value;

4. Then you can delete unnecessary systems;

5. Ok, it will take effect after the restart.