diff --git a/documentation/pestpp_users_guide_v5.1.18.docx b/documentation/pestpp_users_guide_v5.1.20.docx
similarity index 72%
rename from documentation/pestpp_users_guide_v5.1.18.docx
rename to documentation/pestpp_users_guide_v5.1.20.docx
index 9409c38f..91ca95ca 100644
Binary files a/documentation/pestpp_users_guide_v5.1.18.docx and b/documentation/pestpp_users_guide_v5.1.20.docx differ
diff --git a/documentation/pestpp_users_manual.md b/documentation/pestpp_users_manual.md
index 92e092b9..2821063f 100644
--- a/documentation/pestpp_users_manual.md
+++ b/documentation/pestpp_users_manual.md
@@ -1,13 +1,13 @@
 
  <img src="0d3cb7750c90b712af04ea3a51c8ecb968d784cc.png" style="width:6.26806in;height:1.68194in" alt="A close up of a purple sign Description automatically generated" />
 
-# <a id='s1' />Version 5.1.18
+# <a id='s1' />Version 5.1.20
 
 <img src="0e14ec9848f78a9809081572ca785af9990c2d38.png" style="width:6.26806in;height:3.05972in" />
 
 PEST++ Development Team
 
-July 2022
+August 2022
 
 # <a id='s2' />Acknowledgements
 
@@ -70,7 +70,7 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
 
 # Table of Contents
 
-- [Version 5.1.18](#s1)
+- [Version 5.1.20](#s1)
 - [Acknowledgements](#s2)
 - [Preface](#s3)
 - [License](#s4)