First, understand that this modification is for vBulletin 3. This version is several years old and if you're using newer version, this will simply not work.

Second, the 5th step is only necessary if your processor requires the currency symbol. If this is your case, take into account that the template edit that I mention is for another modification (https://vborg.vbsupport.ru/showthread.php?t=125369). This should be clearer to you now.

Oh thanks a lot for answer! Didn't expected at all, i've checked your profile and your last time visit was at 2014 :)

Mine version is 4.23... but i still can't find where to modify the html code you writing in step 5 and 6...

I completed all above, except the optional steps and still see the payment in GBP...
I think you are not using it anymore, right? So may be someone can point me, who did it already for vbulletin 4.23 ?