By the MBR limit, you can have 2TB only.
If you want to increase your disk over 2TB, you must convert MBR to GPT.
In Microsoft, they will ask you to use diskpart to delete volume on your disk, and then convert to GPT.
If you do that, you'll lost all data.
Now, another solution here.
You can use gptgen to convert MBR to GPT without lost any data.
GPTGEN download link: