Regarding o to ue verbs in the 1st person plural conjugation

Hola James

I am not sure which lesson you were looking at (there is nothing linked/attached) to your query...

There are irregularities in certain tenses in Spanish that need to be studied in groups of verbs (e.g. e>i verbs in El Presente, o>ue in El Presente de Subjuntivo, radical change verbs in El Indefinido...etc) 

Once you get to know the verbs and recognise them as one that belongs to this or that group, it starts getting easier to conjugate them. 

Now, you are mentioning the verb Morir in your query. This is a verb that undergoes vowel change o>ue in the present; that undergoes vowel change o>u in the simple past, and undergoes an extra vowel change o>u in the present subjunctive in the nosotros and vosotros form:

yo muera

tú mueras

él muera

nosotros muramos

vosotros muráis

ellos mueran

The same goes for verb "dormir" (to sleep):

yo duerma

tú duermas

él duerma

nosotros durmamos

vosotros durmáis

ellos duerman

These two verbs are studied together because they undergo the same vowel changes in the present, past simple and present subjunctive. 

Morir and Dormir (presente subjuntivo)

Morir and Dormir ( pretérito indefinido)

Poder, despite having the same vowel change as morir or dormir in the present indicative, it is not affected the same way in the Present Subjunctive or the Simple Past.

Saludos

Inma