Use a regex:
\(.+\)
Should do it.
using System.Text.RegularExpressions;
public static Regex regex = new Regex(
"\\(.+\\)",
RegexOptions.Multiline
| RegexOptions.CultureInvariant
| RegexOptions.Compiled
);
...
string result = regex.Replace("AB546DF6G (blabla blalal 4 gfg)", "");