Upgrading 3.5.2 failed; Install Page showing instead

A loss of connection actually should not interfere directly with the update process. Clear your local browser cache and always ensure you have backed up your site (yup, those seemingly annoying warnings you see that so many appear to ignore).

That said, you can find timely posts here on the forum by using the search filters of your search provider. Two year old posts are basically not going to be useful.

What is the risk if I were to proceed with a Manual Update?
I’m quite worried about losing posts/images/etc.

Any help/suggestions, please?

Anyone, please?

What is the risk if I were to proceed with a Manual Update?

Download WP3.5.2, unzip.

Now, perform a full site backup.

Turn off any cache plugins.

Then, using FTP, remove only these two folders:
/wp-admin/
/wp-includes/

do not remove or otherwise edit the folder:
/wp-content/

Upload:

/wp-admin/
/wp-includes/

Clear browser cache. Log in. Check full functionality of site. Turn server cache back on if was in use.

I am unable to turn off any cache as I am not even able to login. I am given the Welcome Page to the installation process.

I have tried steps 4 onwards (according to your steps) but I am still having the installation process shown to me when I tried to go to my wp-admin.

When I tried to go to a known page within the site (eg: Contact Us page), the URL is automatically added with “wp-admin/install.php”. The error is then shown: This webpage has a redirect loop. Error code: ERR_TOO_MANY_REDIRECTS.

When I checked on my site’s error log, this was found:
[28-Jun-2013 00:07:43] WordPress database error MySQL server has gone away for query SELECT option_value FROM wp_options WHERE option_name = ‘_transient_doing_cron’ LIMIT 1 made by _get_cron_lock

But I have no idea what those two errors mean.

I am unable to turn off any cache as I am not even able to login.

Please follow (all of) what I noted above and refer to the Codex for additional support.