The prefix in the word upgrade is 'up'. The opposite would be downgrade.
The prefix un- makes the word "unsuitable."
The true opposite of prefix is no prefix.But, as a prefix means something added at the start of a word. the generally understood opposite is suffix - which is something added to the end of a word.
The opposite is impatient.
The opposite prefix of "incredible" is "cred." The prefix "in-" indicates negation or the opposite, so removing it leaves "credible," which means believable or able to be trusted. Thus, "credible" serves as the antonym of "incredible."
The prefix "dif means the opposite of, or reverse.
The prefix that makes "upgrade" mean the opposite is "down-," so "downgrade" means to lower or reduce in quality or status.
The opposite prefix of the prefix "meta-" is "pre-".
The opposite of median with a prefix is "nonmedian."
The opposite prefix for personal is "impersonal."
The opposite of "thoughtful" with a prefix would be "thoughtless."
The prefix for the opposite of order is "dis-" or "un-".
The opposite of active using a prefix is "inactive."
The opposite prefix of "essential" is "non-essential."
The opposite of judge using a prefix is misjudge.
The opposite prefix of "distinct" is "in-," making the word "indistinct."
The opposite form of the word "expendable" by adding a prefix is unexpendable.
The opposite prefix to "lawful" is "un-," so the opposite of "lawful" would be "unlawful."