Go to the web.config file at the root level:
To increase the IIS Connection timeout value, change the following value
add name="CMSConnectionString" connectionString="Persist Security Info=False;database=xxx;server=xxx;user id=xx;password=xxx;Current Language=English;Connection Timeout=<Increase this value>;" />
OR
Change the below:
<system.web>
<httpRuntimemaxRequestLength="51200" requestValidationMode="2.0"/>
to
<system.web>
<httpRuntime executionTimeout="180" maxRequestLength="51200" requestValidationMode="2.0"/>
This will increase it to 3 minutes.