Hi martinl47003580, you need to use a regular expression based string substitution search/replace:
Find: ^\w*\d*\s
Replace: (blank)
The above regex will look for zero or more letters and zero or more numbers and then a single space at the beginning of the filename.
I have tried to make this expression a little more versatile/robust than your sample filenames which could have used a very simple/explicit expression:
F\d\s or ^F\d\s
However what if you ever had files that started with a different character than an uppercase F? Or what if you ever had two or more digits following the letter before the space? This is why I went with a more flexible/robust expression.

It is usually a good idea to tick the “Preserve current filename in XMP Metadata” when batch renaming, so that you can easily recover the original filenames if required.
EDIT: Looking at this a second time, an equivalent result and perhaps “technically better” would also be achieved with ^\w[0-9]+\s or how about ^\w+\d+\s or perhaps even ^\w+?\d+?\s etc. This is the great thing about regex, there are many ways to get to the same result (some verbose, some more elegant) – it all depends upon the context/use and how flexible the pattern recognition needs to be! Some other variations could be F.+?\s or ^.+?\s
P.S. You can save this search/replace as a preset using the save button at the top of the interface.