I am getting a prebuild PC and i want to upgrade my storage before delivery , i can not find any info about how many m.2 slots are in an Intel h310 Chipset? I want 512GB of storage instead of 256GB , but as i said , i cannot find any info if i can install a 2nd m.2 ssd.
There are none "on" the chipset. You need to ask the motherboard manufacturer how many they have on the motherboard.
You should check the specification of the motherboard rather than chipset. Depends also what kind of SSD are you using. The MVMe SSD requires 4 PCIe lines, while SATA only 2 lines. The H110 chipset supports 6 PCIe lines only, so I don't believe that motherboard is equipped with two M.2 slots.
The PCH has a certain number of PCIe lanes and these are used as necessary to support other components in the system. Whatever number are left over can be used to support M.2 slots (which can consume two or four PCIe lanes). If there is a need for additional M.2 connectors, PCIe hubs can be added to get the additional lanes necessary. Bottom line, what chipset you have does not decide how many M.2 slots there can be. It is a design (and cost!) decision made by the board manufacturer.