The expression $2a - 4a + 6$ can be simplified to $-2a + 6$.

To simplify the expression $2a - 4a + 6$, we need to combine like terms. Like terms are those that share the same variable raised to the same power. In this case, $2a$ and $-4a$ are like terms because both contain the variable $a$.

First, we combine the coefficients (the numerical parts) of the like terms. The coefficients of $2a$ and $-4a$ are $2$ and $-4$, respectively. Adding these coefficients yields:

Thus, $2a - 4a$ simplifies to $-2a$.

Next, we look at the constant term, which is the number without a variable. In this expression, the constant term is $+6$. Since there are no other constant terms to combine it with, it remains unchanged.

Bringing it all together, the simplified form of the expression $2a - 4a + 6$ is:

This process of combining like terms is a fundamental skill in algebra, making expressions easier to manipulate and understand.