Head voice

Hello, I am having a hard time with head voice. Like when we do the exercise yah 

I can only sing about two and the rest is too high for me is there a way to train my voice high without straining too much so my voice can reach that high

i don't have a problem with the chest voice 

Yes! The easiest way to begin training your head voice is by singing on something semi-closed. Try straw singing and lip trills first; you can also try singing on a hum, NN or NG sound. Build that coordination (without straining) and move to vowels later!

Thank you so much for replying back to me!

Just to make sure I'm understanding correctly instead of singing the warm-up YAH I will follow along with that warm up singing hum, nn, or ng correct?

I also have one more question is it OK to practice one hour in the morning and then one hour at night do you think that will help my voice become stronger and better?

Yes, that's correct! Only once the hum, NN or NG is comfortable, see if you can open up to a vowel (like OO, EE, or AH). It's okay to drop out as well! Some exercises may go too high or too low for every singer to comfortably sing. 

2 hours of daily practice is quite a lot! I'd recommend 30 minutes at first, and continue for longer if you're feeling healthy and strong. Be sure to take breaks as well (silence, hydration, listening to music, or singing through a straw, for example).