Download the official installer from https://www.jetbrains.com/idea/download/ and choose the appropriate build (Ultimate or Community) for your platform. The Community edition is free for personal use; Ultimate requires a paid license but offers a 30‑day trial.

Install the IDE using the platform installer. During setup on Windows, enable the 64‑bit launcher and add a desktop shortcut if needed. When upgrading from an older release, choose whether to import settings. To minimize upgrade issues, remove stale caches from the previous version.

• Windows
  • Config: %APPDATA%\JetBrains\IntelliJIdea2019.3
  • Caches/logs: %LOCALAPPDATA%\JetBrains\IntelliJIdea2019.3
• macOS
  • Config: ~/Library/Preferences/IntelliJIdea2019.3
  • Caches: ~/Library/Caches/IntelliJIdea2019.3
  • Logs: ~/Library/Logs/IntelliJIdea2019.3
• Linux
  • Config: ~/.config/JetBrains/IntelliJIdea2019.3 (or ~/.IntelliJIdea2019.3 on older setups)
  • Caches: ~/.cache/JetBrains/IntelliJIdea2019.3
  • Logs: ~/.local/share/JetBrains/IntelliJIdea2019.3/log

Use Help -> Show Log in Explorer/Finder to locate the actual directories on your machine if paths differ.

On first launch, use the Welcome screen to create or open a project. For licensing, open Help -> Register (or Manage Licenses) and choose one of the supported, legitimate options:

• JetBrains Account: Sign in to an account with an active subscription (e.g., All Products Pack or IntelliJ IDEA Ultimate).
• Activation code or license file: Paste the code or select the license file received from JetBrains upon purchase.
• License server: Point to your organization’s official JetBrains Floating License Server (if applicable).
• Free options for personal/educational use: Community edition (free), Educational license (for students/teachers), Early Access Program (previews), or the 30‑day trial for Ultimate.

Configure JVM options via Help -> Edit Custom VM Options. This creates a user‑level copy so updates won’t overwrite your changes. Example settings for a workstation with 16 GB RAM:

# Memory
-Xms1024m
-Xmx4096m
-XX:ReservedCodeCacheSize=512m

# GC tuning (JBR8)
-XX:+UseG1GC
-XX:SoftRefLRUPolicyMSPerMB=50

# UI/font rendering
-Dawt.useSystemAAFontSettings=lcd
-Dsun.java2d.uiScale.enabled=true

# Diagnostic (optional)
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=${user.home}/idea-oom.hprof

Avoid editing .vmoptions files directly in the installation directory; always use the menu action so the IDE manages the correct location and format.

Upgrade paths from prior versions can leave incompatible caches or plugins. If you encounter slow startup or indexing issues after an upgrade:

• Disable incompatible plugins via Settings/Preferences -> Plugins.
• Invalidate caches via File -> Invalidate Caches / Restart.
• If problems persist, close the IDE and remove the cache directories listed above, then restart.

Use JetBrains Toolbox App (https://www.jetbrains.com/toolbox-app/) to manage multiple IDE versions, switch channels, and handle upgrades/rollbacks safely.

If the registration dialog shows "Your activation code could not be validated (error 1653219)" or similar:

• Confirm the license is valid for IntelliJ IDEA 2019.3 and your edition (Ultimate vs Community does not require a paid license).
• If using a JetBrains Account, ensure network access to JetBrains licensing endpoints; check proxies, corporate firewalls, and SSL inspection policies.
• Verify system date/time and timezone; large clock skews can break TLS and license validation.
• If your organization uses a license server, confirm the URL, server health, and that a seat is available.
• For offline environments, use a legitimate activation code or license file obtained from JetBrains; avoid third‑party tools or agents.
• Update to the latest minor build of 2019.3 or a newer release, as licensing components are periodically improved.
• If the issue persists, capture logs via Help -> Collect Logs and Diagnostic Data and contact JetBrains Support with details.

General tips:

• Keep installation paths ASCII‑only to avoid issues with tooling that may not handle non‑ASCII paths well.
• When switching major versions, prefer reinstalling and importing settings rather than copying installation directories.
• Backup keymaps, custom code styles, and inspections via File -> Manage IDE Settings -> Export Settings.