Hi! I'd like to do such replacement:

The primary task is to locate "</span>" which is not appear in pairs.
Note the "</span>" in line 3, line 5, line 7. They should be cleaned off.

*SOURCE:
1. <p><span style="font-weight:bold;">CCNA Portable Command Guide</span></p>
2. <p><span style="font-weight:bold;">Second Edition Scott Empson</span></p>
3. <p>Cisco Press</span></p>
4. <p>800 East 96th Street Indianapolis, Indiana 46240 USA</p>
5. <p>Command Syntax Conventions</span></p>
6. <h1><span style="font-weight:bold;">PART I</span> <span style="font-weight:bold;">TCP/IP Version 4</span></h1>
7. <h2>CHAPTER 1</span><span style="font-weight:bold;"> How to Subnet</span></h2>

*RESULT:
1. <p><span style="font-weight:bold;">CCNA Portable Command Guide</span></p>
2. <p><span style="font-weight:bold;">Second Edition Scott Empson</span></p>
3. <p>Cisco Press</p>
4. <p>800 East 96th Street Indianapolis, Indiana 46240 USA</p>
5. <p>Command Syntax Conventions</p>
6. <h1><span style="font-weight:bold;">PART I</span> <span style="font-weight:bold;">TCP/IP Version 4</span></h1>
7. <h2>CHAPTER 1<span style="font-weight:bold;"> How to Subnet</span></h2>

Would anyone please teach me how to do this task using a Regular Expressions ?
Thank you!