A guess is an answer made without any knowledge of the problem, or consideration of relevance. If you answer "58" without even knowing anything about the field of the question, that is a guess. Any answer that doesn't take into account the details presented by the situation, is a guess.
An hypothesis, is an educated guess. I give a possible explanation based on the information available. Ex.: My friend shut a suitcase; there were 2 clicks, and we need to get the case open again, but the friend is in shock over what he found inside. My hypothesis for getting it open again without his help is that the combination lock on the suitcase is off by just one combination digit because one click was the latch, and the other click changed the last digit in the combination.
A theory is a hypothesis that has been tested repeatedly for virtually every variable that can be imagined and has still held true. This makes it generally accepted as true, but not necessarily proven. The Theory of Relativity has been tested for many variables and still holds true, so it is generally accepted to be true, however it can still be proven false if a test reveals that there are circumstances where approaching the speed of light does not slow the passage of time.
A guess or conjecture is an attempt to form an opinion based on speculation or incomplete scientific evidence. A hypothesis attempts to answer questions by putting forth a plausible explanation that has yet to be rigorously tested through suitable experiments or facts. A theory, on the other hand, has already undergone extensive testing by various scientists and is generally accepted as being an accurate explanation of an observation. A theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. A theory is valid as long as there is no evidence to dispute it. Therefore, theories can be disproven.