This game (as most others, even actual ones), is a 32 Bit game. 32 Bit games can usually only address 2 GiB of RAM and NOT 4 GiB! This is because 32 Bit Software uses usually only the positive part of signed 32 Bit Integers, so you loose 1 Bit because of the sign and you get 31 Bit => 2 GiB.
Some software can be patched (with the patcher posted in this forum for example) to use the whole 32 Bit Integer to address, but if it wasnt build to do that (in this case it would be usually already patched), then this can lead into odd behaviour or crashes for example. This patch doesnt make the game 64 bit, it would still remain to be 32 bit.
There even exist another way to address more than 4 GB for 32 Bit software, but this one is even more likely to crash or to produce odd behaviour, especially if the software wasnt build to use it, so I dont go deeper into it.
Also it isnt really possible to make a 64 Bit Software out of a 32 Bit software, without recompiling it completely and maybe usually even not without rewriting the source code of it. Btw. does 64 Bit software not only differ in the way, that you can address more RAM, but it differs also in the way that another instruction set is used.
Finally, you cant do much about this and I wouldnt even recommend to use this patcher for it, especially because I doubt that the game even would use the extra amount of RAM (maybe it even doesnt use more than 1 GiB).