The easiest and most common way to say it: "Anímate!" (Ah-NEE-mah-teh) with the strongest pronounciation in "ní" or "nee". It's like saying "Cheer up!". What the others have commented is also right: "Vamos, tú puedes hacerlo!": Come on, you can do it! "Vamos, vamos!": Let's go! let's go! But when it comes to "Cheer up" the most accurate translation would be "Anímate!". And also, I saw your comment asking about one that sounds like "alegrase, alegrasa", and It would be "Alégrate" which is also like "Cheer up", "rejoice". And If you'd like to be polite, instead of "Alégrate", use "Alégrese" (When talking to older people, people you respect, etc), but again... "Anímate" is more common. :) Alégrate: Ah-leh-grah-teh. (Again, the accent becomes stronger in the "lé") Alégrese: Ah-leh-greh-seh. (Accent is stronger in "lé") Have a nice day! :)

¡Vamos, tu puedes hacerlo!

That's not the easiest way to say it (the answer from Linda). The easiest and most used is: Ánimo! And you also use it with children if they're sad. Ánimo! Todo se pondrá bien. :)

@eliezer is there any pronounce as 'alegrase or alegrasa' ?

Hay muchas formas de alentar en español , las más comunes son : Vamos,Vamos!, Tu puedes hacerlo! , Eso Eso! y otras :P