Conversion: shorten a field

I am sorry if this looks trivial question to some/most of you but I decided to call for help after having read thhe help and was unsuccessful in all trials.

Can someone please tell how do I supress or change word(s) in a tag?

Example, asune my title tag is

"this is a long title"

and I want to change it to

"was a long title"

or

"short title"

Thanks for your time

The examples do not really help.
As there are so many methods to modify data, it depends a lot on the data structure.
E.g. if you simply want to replace "This is" with "was", then use an action of the type "Replace".
If you want to cut the data to a certain length, regardless of the contents, then an action of the type "Format value" with a string function like $left(%title%,15) might be enough.

Thank you,
I tried
$replace(%title%,this is,was) as in the help example:
$replace(%artist% - %album% - %track% - %title%,_,-)

but this did not change the selected titles

I could successfully use cutleft though

Starting to think that this is reserved for people with much higher iq than mine...

Where / in which context did you try the $replace() statements?
You would have to use an action of the type "Format value" for TITLE (or the Convert>Tag-Tag function).
The first parameter of the $replace() statement is the source string, not the target.
So, I am sure that
$replace(%artist% - %album% - %track% - %title%,_,-)
has worked - only that there was no target specified where to put the result.

Also, it is not necessary to use the scripting functions as there are at least 2 Replace-actions that guide you through the parameters.