If they are within the same row, then that just comes down to experience as some of the others have said. With practice and more practice, your tension will 'even' out. Unless I'm wrong, and you've been knitting for years, but it's usually something that happens to us all when you start. You could experiment with wrapping your yarn around your fingers in different ways, to see if this helps with your tension, but really, it will come with time.
To even them out, you just use your needle tip, or any other sharp pointy thing, to adjust the stitches beside them. Just insert said tip into the strands of the stitches beside the uneven stitches, starting with the closest ones, and give a little lift on the needle, to pull some of the yarn from the large stitches, into the smaller stitches, until you like the look of the large stitch. The extra yarn you have just moved will be sticking up out of the stitch you just manipulated, move onto the next strand next to this one and do the same thing. Keep doing this to each strand, moving away from the uneven stitches, until you have redistributed the yarn into the other stitches to get the result you desire. You will have less and less yarn to move each time until you end up with none left to really manipulate, and your stitches should look more even.
Not sure if this is really a clear explaination, but I don't really know how else to put it.