Go to “Functional Administrator” responsibility à Select “Core Services” (If missing, assign ‘Functional Administrator’ responsibility to your account)

OR

Select “Caching Framework”
Select “Global Configuration”
Now click on “Clear cache”
Click on “Yes” button to confirm
Click on “Apply” button to clear the cache

 Source: How to Clear the Cache Using Functional Administrator? (Doc ID 759038.1)

 Note: If you have removed the _pages manually and are facing login issue that’s blank screen.
Use the ojspcompile.pl perl script to perform a manual pre-compilation of the JSP pages.The following command will compile all the JSP pages and build up the JSP cache again.

            perl $FND_TOP/patch/115/bin/ojspCompile.pl –compile –flush -p 2

This utility is also used by the AD utilities to perform this action such as when patches are applied that replace one or more JSP pages

See Note: JSP Pages Hanging in R12 After Removing Cached Class Files in _pages (Doc ID 433386.1)