Normally, I argue against an infinite regress of sustaining causes of change in support of the Aristotelian-Thomistic argument. However, the following argument is logically valid:
1. Everything that changes has an external cause. (Premise)
2. The universe changes. (Premise)
3. Therefore, the universe has an external cause of its change. (From 1 and 2)
Premise (1) simply reiterates that no potentiality can actualize itself. If it could, then it would be self-caused, and would be existent and non-existent simultaneously, which is absurd. Premise (2) is obviously true, barring some radical version of metaphysical skepticism.
The only objection truly worth noting is the idea that the argument commits a composition fallacy. Just because every part of a mountain is small doesn't mean the mountain as a whole is small. Likewise, it is surmised, just because every part of the universe has an external cause of its change doesn't mean that the universe as a whole has a cause of its change.
I think this objection is dubious at best. After all, an explanation of the change in every part of the universe would not explain why there is any change at all to begin with. Moreover, many times the whole is like its parts. If every part of a mountain is made of rock, then the mountain as a whole is made of rock. Sticking with this analogy, we know that the mountain as a whole has an external cause, e.g. the accumulation of various geological processes.
I think the argument summarized above most resembles the latter type of part-to-whole relationship. If I'm correct about this, then we have an argument for an Unmoved Mover, which exemplifies no potentiality. It must, therefore, not only be immutable, but purely actual, eternal, indestructible, unique (for to differ from actuality is to be non-actuality. Other things are distinct insofar as they exhibit various levels of potentiality), as well as omnipotent, omniscient, and morally perfect. In defense of these three latter attributes, if the Unmoved Mover were limited in any of these respects, that would entail potentiality, which is impossible for the Unmoved Mover.
*Update: Given that the universe as a whole exhibits both actuality and potentiality, it follows that we have an even stronger argument against the composition fallacy objection. Since no potentiality can actualize itself, and the universe exhibits potentiality, it necessarily follows that the universe as a whole must have its potentiality actualized by some external cause. This could only be a timeless, changeless (for time is a measurement of change), immaterial, and very powerful entity, e.g. the Unmoved Mover.