Sentence tenses, whether past, present or future, are dictated by the tense of the verb you write. How you change the tense of a sentence from past to present depends on the form of past tense being used. The four possible tenses are simple past, which is most common, followed by past progressive tense, past perfect tense, and a combination of both of those, past perfect progressive tense. Each of these tenses has a present-tense counterpart. By slightly modifying the verb, you can change the sentence from past tense to present tense.
Change the simple past tense to the simple present tense. For example, a simple past-tense sentence that reads "I smiled" can be changed to "I smile," which is simple present tense.
Change the past progressive version of the sentence to the present progressive. For example, changing "I was smiling" to "I am smiling" will change the past progressive tense to present progressive tense.
Change the past perfect tense to the present perfect tense. Instead of "I had smiled," write "I have smiled."
Change the past perfect progressive tense to the present perfect progressive tense. For example, change "I had been smiling" to "I have been smiling."