Video tutorial

Launch DC-Unlocker client software.

Open Server tab, enter your username and password that you received after credits purchase. Click "Check login". (you can buy credits here www.dc-unlocker.com/buy).
If DC-Unlocker/Vygis/Rocker/Infinity dongle is connected, do not enter username and password, only click "Check login".

Note: if you can't login or get error connecting to server after connecting Huawei E586 to PC, check these settings here.

Select manufacturer: Huawei modems, model leave as Auto detect (recommended).
Press "Detect" button (Big magnifying glass):

Open Unlocking tab, click “Unlock”.

After you see that device was successfully unlocked, restart it by disconnecting and connecting back. Now you can use it with any SIM card.