Better to replace as soon as possible, it's ok to replace one tire if the other tire in front is still in good condition. replace it with the same series.
Ok kung the same brand pwede din hindi, for example, kung yung series or specs ng gulong mo sa kabila eh 205/70/16, ganun din ang ipalit mo para balance, bsta yung harap parehas, wala ko idea bro diyan sa las pinas, better to canvas 2-3shop na makita mo diyan and then compare mo na lang yung prices
Ideally, both front or both rear (as the case may be) should be replaced. However, if the other tire still has about 80% tread life, you can get away with just replacing one tire.
Tire compound and tread pattern can have an effect on drive-ability. Because of this, both tires should be of the same make, model and dimension. It's typically not wise to use a different brand or model of tire even if it's of the same dimension.