VTTSX (the 2060 fund), as you may know from the Vanguard fund page, is made up of a certain percentage of domestic and foreign stocks and bonds.

VASGX has the same funds but with different allocations. Unlike the Target 2060 fund, it won't use a glide path (won't become less aggressive over time as you approach retirement.)

(And both these funds already own VTSMX as their largest holding. You've already invested in it.)

If you are using a Target Date fund and want to be more or less aggressive, I'd just change which fund you are investing in. If you want to be less aggressive for some reason, move to Target Date 2055. Or more aggressive, move out.

But you're already balanced. That's the great thing about those Vanguard funds, they're always heavily diversified.