Get it from the download page.

Here are the most noticable changes and new features:
* 64 bit version allows HeidiSQL to use much more of your memory than the 2GB in 32 bit mode
* New feature: Fast table status for databases with InnoDB tables. (Disable Session > Advanced > [X] Get full table status)
* New feature: Favorites in database tree
* New feature: Append parameter names for procedures and functions in completion proposal
* New feature: Compressed .sql file export
* Migration to the brand new Delphi XE 5 compiler
* Replace out-dated code which partly not runs in 64 bit mode
* Update gettext unit
* Update Cromis.DirectoryWatch unit
* Update VirtualTree component code to 5.2.1 (r567)
* Update SynEdit component (r114)
* Revert r4538 (ctrl backspace bug), as this broke tabbing through grid cells
* Add fallback "DELETE FROM..." to CSV import dialog's option "truncate table"
* Fix non-working "Replace all" button on search/replace dialog
* Turn "Drop" confirmation dialogs into custom critical types, and set focus to the Cancel button.
* Quote plink.exe path and file in SSH tunnel preparation, so spaces in the path do not break the CreateProcess call.
* Fix quick filters, broken with formatted numbers
* Prefer Delphi's various TGraphic descendants over the out-dated GraphicEx library. PNG images even show their transparency now. Removes support for the myriad of exotic image formats.
* Restrict "Quick filters" > "More values" submenu to tables with less than 1GB of data, so we're not running into an endless query
Phew. And for the nerds: watch out for *all* changes here.