Upgrading Drupal

I have a Drupal 7.56 website that is currently running on PHP 5.3.  I have downloaded PHP 7.2 and plan to install it, but how do I tell DRUPAL to stop using v5.3 and start using v7.2?

Hello,

I just upgraded from Drupal 7.2 to 7.56
I now have an error that appears "User warning: The following module is missing from the file system: tb_megamenu." in _drupal_trigger_error_with_delayed_logging () (line 1143 in / home / ....

I tried to search the net but I can not find
If I understand correctly, this is the default theme, but how to correct this error?

Thanks for your help

I have a site that I created using Drupal version 8.4.2. I have since created a different site using 8.4.4 and decided to get all my installations running on the same version, espcially since neither of them have been deployed to production yet. Both websites run fine on my machine in their initial versions. I am using PHP 7.1 installed on a Windows 10 machine, i.e. using IIS.

I know 6.x sites are very fast.

I made a website using 7.x version with many Views but it was tremendously slow. I worked 2-3 years on it to make fast and finally I've laid it off to die.

I've a very successful site on 6.x now will upgrading to 8.x will kill its speed? How slow it could become if I upgrade without any changes?

Is it possible to run 6.x to run on Ubutu 14 or 16?

Will any issues come? and how to solve them?

After upgrading from D7.50 to D8.4.4, the database contains these tables:

- migrate_map_5a...[lots of characters] (about 20 items; all with zero size)

- migrate_map_d7_[some kind of machine label, such as "menu"] -- there are a few dozen of this kind, some being empty and others of varying sizes ranging from 1 to about 55 (the one about "blocks")

And there is a similar pairing (lots of characters vs specific machine labels) with the prefix "migrate_message". These ones are mostly empty (zero size).

Anyone tried deleting these?