I comfortably sing alto with my chest voice.  I cannot seem to access my head voice without my throat tightening up and only getting squeaks out.  I've done the head voice tutorials, but I don't seem to able to figure out how to access mine without my throat tightening.  Any suggestions? 

I hear you! You're certainly not alone. Have you watched this "head voice troubleshooting" livestream from Abram? https://www.30daysinger.com/tutorial/head-voice-troubleshooting/1

My favorite tools to access head voice function without squeezing are a hollow "cuckoo clock" sound, an owl hoot, and a dopey character voice (think Patrick Star from Spongebob). All of these sounds encourage a lower larynx position, which discourages squeezing and helps us "flip" into head voice. They can also get us out of "singing mode", which can be helpful if the pressure to find head voice and sound "good" are causing you to squeeze up. I cannot stress this enough: head voice doesn't have to sound good in the beginning, and it's probably going to be weak and breathy. That's all normal!

If none of those sounds are working well for you, semi-closed exercises (especially singing through a straw) can be helpful. 

Let us know how it goes!