How do you make a top bigger?

I got this top and its slightly too small and I wanna make it bigger, how do I stretch it?

You can't make it bigger...unless you get some of the exact same fabric and some how sew it on.
Take it back to the shop you got it from and ask for a bigger size.

if you put it on it will stretch it out

Depending on the material you can literally stretch it by pulling at it where it is too small. But once you wash it it will likely go back to shape. This may ruin it and stretch it out of shape a bit. Otherwise get a bigger size or get a bit skinnier...