Essentially the two versions features wise are the same, there may well be optimisations/improvements and or bug fixes in the later builds. So what ever features and functions (shields, etc.) that you used in 7.0.1426 you should use in 7.0.1456.
You may want to consider a clean install rather than an update install (export your settings first to save any changes you made), for those that had any problem with 7.0.1456 (I didn't, luck me) seemed to be related to an update rather than a clean install.
- Download the latest version of avast, 7.0.1456
http://files.avast.com/iavs5x/avast_free_antivirus_setup.exe and save it to your HDD, somewhere you can find it again (if you didn't save your last download). Use that when you reinstall.
- Download the avast! Uninstall Utility, aswClear.exe
find it here and save it to your HDD (it has uninstall tools for 5.x, 6.0.x and 7.0.x).
- 1. Now uninstall avast! (using add remove programs, if you can't do that start from the next step), reboot.
- 2. run the avast! Uninstall Utility from safe mode, first for 6.x if previously installed and then for 7.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.