在英语中，复合句是由一个主句和一个或多个从句组成的句子。

要改变复合句，可以采取以下几种方法：

1. 将复合句改为简单句：删除从句，只保留主句。例如：“I will go to the park if it doesn't rain.” 可以改为：“I will go to the park.”

2. 将复合句改为并列句：使用连词（如and, but, or）将两个简单句连接起来。例如：“I will go to the park if it doesn't rain.” 可以改为：“I will go to the park, and it won't rain.”

3. 将复合句改为分词短语：使用现在分词或过去分词形式来表示从句的动作。例如：“While I was walking in the park, I saw a bird.” 可以改为：“Walking in the park, I saw a bird.”

4. 将复合句改为定语从句：使用关系代词（如who, which, that）将两个简单句连接起来。例如：“The book that you gave me is very interesting.” 可以改为：“You gave me the book, which is very interesting.”

5. 将复合句改为状语从句：使用副词或副词短语来表示从句的动作。例如：“Although it was raining, I went out to play.” 可以改为：“In the rain, I went out to play.”要改变复合句，可以根据句子的意思和结构选择合适的转换方法。