to increase shared gpu memory

I really want your help in this question rapidly     laptop : dell inspiron 15 3576              cpu : i7-8550u               ram : 8 gb                    2nd gpu : amd radeon 520                       my problem is that  I am playing a gme requiring high hardware performance  i shot task manager during play and i found that vram of radeon gpu is 2 gb can increase up to nearly 6 gb so there is about 4 gb shared gpu memory . i want to know how I can use this shared gpu . please answer me rapidly and if you say  i cannot allocate part of physical memory to vram on my dell inspiron (as i am gonna buy another extra  8 gb ram ) so tell me how i can get benefit of this shared memory because it is not put here for joke and dell company installed an external gpu in their laptops which can get shared memory they didnt do that for joke also so for sure this shared memory can be used .please understand me and anwer me . thanks