# our old man was crucified with him

"our sinful person died on the cross with Jesus" 

# old man

This means the person who once was, but who does not exist now.

# the body of sin

"our sinful nature" 

# might be destroyed

"might die"

# we should no longer be enslaved to sin

"sin should no longer enslave us" or "we should no longer be controlled by sin"