What this problem is
Your site returns 500 after activating or updating a theme.
Why it happens
- Fatal PHP error in theme code
- Theme requires a newer PHP version
- Missing required plugins for the theme
Prerequisites
- FTP/File Manager access
- At least one default theme installed (recommended)
Diagnosis
Check logs for file paths under wp-content/themes.
Detailed steps
Step 1) Switch to a default theme
Rename the active theme folder. WordPress will fall back to a default theme if available.
Step 2) Fix PHP version compatibility
Switch PHP version in hosting panel to meet theme requirements, or use a different theme.
Step 3) Update theme safely
Install the latest stable version and re-test.
Expected results
- 500 removed and site restored
What to do if it fails
- If no default theme exists, upload one (twentytwentyfour) then retry
- Ask host for the exact fatal error line
Best practices
- Keep a default theme installed
- Test theme updates on staging