ClearAttributes

ClearAttributes[symbol,attr] removes attr from the list of attributes of the symbol symbol. 

ClearAttributes["symbol",attr] removes attr from the attributes of the symbol named "symbol" if it exists.

ClearAttributes[s,{attr1,attr2,…}] removes several attributes at a time.

ClearAttributes[{s1,s2,…},attrs] removes attributes from several symbols at a time.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.