Atenolol is excreted mainly by kidney while
metoprolol is metabolised mainly by liver. Therefore, the dose of atenolol should be reduced in patients with renal impairment while the dose of metoprolol should be reduced in patients with liver impairment.
Both of them can be used to treat hypertension, but in different dose. They are pretty similar when it comes to side effects.
Hope this can help.