We started as a .co A while after we bought the .com Now we are considering if we should change everything we've built to the .com domain Are there any benefits in terms of SEO or similar?
Frank Michlick is correct when he says that your .CO would be treated by Google as a gTLD (i.e. like .COM) rather than as the country code for Colombia. So there would be no SEO advantage that I'm aware of in switching to .COM.
That doesn't mean that there is no reason to switch to .COM. After all, SEO isn't the only factor.
Usually the biggest disadvantage to .CO is that the extension is misremembered as .COM, which can result in customer confusion and traffic leakage to another website or non-resolving page.
Now that you have purchased the .COM, you are able to plug the leak by means of a redirect. So that .CO disadvantage is curable without a full-fledged changeover to the new domain and .COM rebrand.
Another potential disadvantage to .CO is that it sometimes looks like a cheap second choice, which affects brand credibility. More often than not, the biggest, most established, and trustworthy brands use .COM. As consumers, we're trained to instinctively spot flimsy websites BEFORE we visit them; so we respond differently based on the TLD.
After all, if a brand / website / company is cutting corners with its most visible identifier – the domain – then what other issues are they neglecting? We have that gut reaction to domains with hyphens, misspellings, or 2nd-choice suffixes. And, although it is merely a gut reaction, it is rational as a general rule, since it is reinforced by the broader population of websites.
Rebranding as .COM might make the brand appear more reputable. Depending on the name itself, that might be more or less important. I think some .CO domains look fine, actually. I can give my opinion on yours in about 60 seconds.
There is some short-term cost in changing over to .COM after having already built on .CO. Meanwhile there is some long-term benefit from a branding perspective. You'll have to weigh that tradeoff. Since you already purchased the .COM, though, my thought is that you ought to use it fully.