How can a man (i.e., Yeshua) become G-d?

He can't! Yeshua did not become G-d. Rather, G-d became a man (Yeshua). Although at first glance this may seem like a concept foreign to Judaism, a deeper look reveals that G-d appeared in human form a number of times in the Old Testament (Tanakh). For example, Genesis 18:1-14; 32:24-30; Exodus 24:9-11; Proverbs 30:4. Thus, G-d came to earth in the form of a man—Yeshua the Messiah. After all, he's G-d so he can do anything. In addition, the Messiah is referred to in Scripture (Isaiah 9:6) as being divine. He is called "the mighty G-d, the everlasting Father."

Additional information can be found in the book "The Death of Messiah".