No, you can't..
Not from 1.7.29 to 1.8.19 directly via OTA.
With ota, you need to update 1 by 1, 1.7.29 - 1.8.5 - 1.8.12-1.8.19. It's because you'll (probably) miss out on some lib files and other stuff..
You'll be much better of flashing the latest full rom. If you do MIUI backup of all your stuff before wiping everything and flashing, you only have to re-arrange widgets when you've restored the backup on 1.8.19
And you will also have a much better, cleaner ROM...