folakas - Thank you for joining PSG. While extremely important, the question you asked is also basic and written in overly general terms. For example, you haven't told us what photo editing software you know how to use, whether you need to enlarge one picture or a thousand, or even why you need to enlarge it (eg, to make a print or for FB), etc. etc. These are important considerations.
This subject and its variants have been discussed tens, if not hundreds of thousand times on the net. Many wonderful tutorials are already available, so there's little point in us repeating or even attempting to summarize the same information here.
Let me suggest that you start by first Googling {how do i make a photo larger}. If you want to do it using photoshop, just add the word, "photoshop" to the search. If you want to use other software, just add the appropriate name. If you want to do it using an on-line service, just add, "on-line" to the search. If you want a video tutorial, just add those words to the search, etc.
If you have any questions after you have read some articles or watched some video tutorials on the subject and have specific questions, feel free to drop back and we'll certainly try to help you.
Tom M