Upgrading Drupal

I have a Drupal 5.3 based website.
Should I upgrade to 5.4 and then 5.5? or directly to 5.5?

It seems there have been some changes to the way taxonomy works, but I can't find any documentation of it. Does anyone know where we can find details?

Hi
I have a vocablulary, with a single term.
It is set to "herarchy : single" and "required" is checked.

So when user submitted content before 5.4, the single term was selected by default, user didn't had to change it.

Now the behavior is different, the taxonomy selection shows "please choose".

I find this to be less intelligent behavior, since there is only one term that I want selected by default and nothing to chose from.

I am in the middle of trying to convert my site from 4.7 to 5.5. I have 1 main site, and 2 sub sites. All worked well with 4.7.

When I did the upgrade, my main site went well.
However any sites I had set up as multi sites error on running upgrade.php. The error I am getting is

Fatal error: Call to undefined function user_access() in /home/ycim/public_html/includes/menu.inc on line 1376

I have the Rogue trailing slash in my User Profile Page - which makes it impossible to show a Default image for user profiles.

This "/" does get overwritten After you submit a new photo. - Strange...

Do you happen to know where I can find this "/" and remove it?

- Thanks

I got this error after updating:

include_once(./modules/statistics/statistics.module) [function.include-once]: failed to open stream: No such file or directory in /public_html/includes/bootstrap.inc on line 512.

Any idea what wrong?