I do not understand it, since it is VPS, it should be scalable, so you should be able to choose the amount of RAM memory or if it has already been chosen, there should be no problem with buying / choosing an additional one.

BTW what operating system is on this VPS - I was looking for lightweight Linux distributions https://itsfoss.com/lightweight-linux-beginners/ and it is very difficult to find one with 256 mb of ram .... but as it turned out it is possible .. ..