By default, RouterOS runs with an evaluation version that is capped at 1 Mbps. You can obtain a 1 Gbps license for free; all you need to do is specify the username and password that you created during registration at Mikrotik.com.
Switch to System | License and click Renew License. You need to fill in your username and password and the desired license type. P1 is a 1 Gbps license, P10 is a 10 Gbps license, and P unlimited has no cap at all.
Once you have configured the username and password, you should see that you have successfully obtained a trial license: