We can see "have + past participle". it means those sentences are using "Present perfect tense". "Present Perfect tense" is used to talk about action which started in the past and continues up to the present. Thus, the correct answer is the 1st one. :)

The 1st as you're actually talking about present.

Thanks, but it is a fact isn't it?. won't it mean another thing if I am using the past tense?. won't it mean studying is hard now, but it is not hard in the past if I am using the past tense in the sentence?.

Elena's answer is good and correct, but it is possible to make a sentence that the other one works for. . Years ago, when I was young, I studied at university. At that time, I found study so difficult, even if it was only 4 hours a day. Since then, I have realized that studying was not hard. . But, you see the normal meaning is as Elena says, present tense.