Master Boot Record (MBR) disks are limited to four primary partitions. This has been a problem for about three decades, but a workaround was invented long ago: One of the primary partitions can be used as an extended partition, which serves as a placeholder for an arbitrary number of logical partitions.
Thus, the solution to your problem is to convert one of your existing partitions from primary form to logical form, thus creating an extended partition. You may then need to resize the extended partition to cover the available space, whereupon you'll be able to create as many additional logical partitions as you like.
Unfortunately, without knowing more about the details of your partitions, I can't advise you about which partition(s) to convert to logical form or what other steps you might need to take. (There are a number of limitations and caveats in such a procedure, but they all depend on details of the starting point.)
Certain third-party Windows tools can do such conversions. The only one with which I'm familiar in any detail is my own FixParts, but it's good only for the primary-to-logical conversion, not for creating new partitions, resizing partitions, or whatnot. You'll need to use some other tool for those operations, and I'm not familiar enough with the Windows utilities landscape to make any recommendations. (FixParts is cross-platform; I'm mostly a Linux user myself.) I recommend avoiding Windows' built-in tool for these operations, since it tends to be flaky and may do more harm than good.
If you want more advice, please post partition details, such as a screen shot of the Windows partition tool showing your partitions and a brief description of what each partition is.