When parentheses are preceded by a plus sign (+) simply remove them; when parentheses are preceded by a minus sign (−) change the sign of every term within the parentheses:
\begin{align} a+(b+c) &= a+b+c \\ \\ a+(b-c) &= a+b-c \\ \\ a-(b+c) &= a-b-c \\ \\ a-(b-c) &= a-b+c \\ \end{align}