Aliens could look remarkably similar to humans. This does not necessarily mean that they would. There are several ways similar species could arise. If the universe is indeed infinite then another species resembling ourselves and other creatures from our planet would be inevitable. Evolution generally utilizes the same tools in different organisms with similar roles. If a planet had an environment like that of the Earth then it is highly likely any life could follow similar, if not the same, evolutionary patterns. The sheer vastness of space implies that many different types of life will be discovered.
On a small rocky planet, covered in liquid water, a mostly oxygen atmosphere circling a yellow star, the only know life exists. If another planet exists matching this basic description, life may likely evolve like life here on Earth. When organisms must adapt to live in a similar environment, many attributes are often similar. Nearly all life on earth resembles each other in many ways. Plant life typically all have roots, stems and leaves. Hearts and lungs are basically standard on oxygen breathing earth life. Although beautifully diverse and appearing incredibly different, life mostly works the same. It is absolutely possible for life on another planet to resembles us, but maybe not likely.
Life evolves according to conditions; under other than Earth-like conditions life would almost certainly appear radically different than life as we know it. Currently, planets like Earth number only one. Planets unimaginably different are being found abundantly. None of these planets so far seem likely to hold life. That is to say that none of these planets have earth-like conditions. If life exists under different circumstances perhaps these planets should be looked at more closely. Until humans have some evidence that life could flourish in different environments than like that of the earth, we will probably only closely consider planets like this to search for life. This fact alone makes the discovery of aliens that look like we do to be more likely. Almost everyone agrees that the universe in infinite and expanding. Seemingly contradictory, this stacks the odds hugely in favor of human like aliens. With an infinite universe everything is inevitable.
Presumably, life in space is as diverse and plentiful as on Earth. Some aliens could look like us, while others are unimaginably different. Would aliens look like us? If they need to.