The systems are configurable only to those Dell has offered.  If you do not see the configuration you want on Dell's own website, check with local resellers or retailers - they may have the configuration you want.  You cannot, however, alter a pre-existing configuration a la carte -- i.e., you cannot add the larger battery to a configuration that doesn't list it.

It depends on whether (or how many) of these are built with the low resolution screen and larger battery.  In theory, it's possible to purchase a new Subaru Crosstrek in the US with a manual transmission -- but good luck finding one. 

 But why would it show up in the specifications then? It means that it would exist right? I tried every combination possible but can't find one with the bigger battery

Thank you very much for the help so far, but would the base version (the one I have to take with the FHD screen) come with the bigger or the smaller battery? I don't think this is very clearly stated within the specifications. 

If it's the first one you've listed, no -- that has the smaller 56 WHr battery.