26 year old with about 500k in a Merrill Lynch Trust Fund, trying to figure out whether to make a change

I know the standard advice here is to put your investments into an index fund, but I'm starting out somewhere slightly different so I wasn't sure whether that applied. The short version is this:

Five years ago, I gained access to a trust fund that was set up for me as a kid, in the amount of about $550k (currently). The same person has been managing it for the last 10 years or so, and doing what I think (?) is a good job - annual growth of about 7-9% per year after fees. Part of the issue is that I'm not quite sure what a good rate of return is (Googling keeps suggesting 12%, which seems super high to me, but maybe not?).

In any case, I've been kinda enjoying having someone else do all the work, not worrying about it except for a check-in call a few times a year, and occasionally taking out small amounts to do things I couldn't otherwise afford ($2k to take my girlfriend on an overseas trip, for example; never more than $5k a year). That said, I realize this isn't the most responsible approach.

What I'm trying to figure out is whether I should be moving all that money into a Vanguard fund, some other investment fund, or something totally different I don't even know about, or whether the current (good? decent? bad? again, don't really know) results justify staying hands-off. In particular, I want to emphasize that I'm not interested in spending a lot of time and effort day-trading or taking a super aggressive, hands on approach to investing, and that peace-of-mind is a major (though intangible) asset for me.