To change the stem u take the word whether it's an o - ue , e-ie , or e-i and take the letter closest to the end and switch it out with the stem change. The stem change only works with verbs that are conjugatedThe e-i is specifically for the ir verbs. With an exception of preferir, referir , and sentir (e-ie)For example Ustedes Almorzar ~ Almuerzan; Yo Preferir ~ Prefiero There is NO stem change in the Nosotros(as).Refer back your notes given by Mrs.Mayo that show you what each stem change for each verb is.