how can i upgrade macbook pro early 2015 version

A MacBook Pro (Retina, 13-inch, Early 2015) can run the latest version of macOS 12 (Monterey), but no higher.

macOS Monterey is compatible with these computers - Apple Support

If your goal is to maximize compatibility with current application software, you want to upgrade to Monterey. When Apple releases Sonoma this fall, anything older than Monterey will no longer be one of "the most recent three", and someone running Big Sur (or earlier) may find themselves locked out of new application software from companies like Microsoft and Adobe.

Monterey is your only choice if you want to run the latest version of DaVinci Resolve – 18.5.1. After poking around, II finally found release notes on the BlackMagicDesign site. They say that the Minimum system requirements for Mac OS are:

• macOS 12 Monterey
• 8 GB of system memory. 16 GB when using Fusion.
• Blackmagic Design Desktop Video version 12.0 or later
• Integrated GPU or discrete GPU with at least 2 GB of VRAM
• GPU which supports Metal or OpenCL 1.2

By default, the Mac App Store hides old versions of macOS, such as Monterey. To get Monterey, use the App Store link on this Apple Support page:

How to download and install macOS - Apple Support

Looking at the DaVinci Resolve system requirements, and MacTracker's description of the 13" Early 2015 MBP, I see a possible problem. That MBP has an Intel integrated GPU that can use "up to 1.5 GB shared from main memory". The DaVinci release notes say you need an "integrated or discrete GPU with at least 2 GB of VRAM."

If that's a strict requirement, and not just a general guideline, you might not be able to run the software on that MBP. Theoretically, the OS could allow the integrated GPU to use more RAM, but I suspect the 1.5 GB limit is wired in at a very deep level where there is effectively no way to raise it.

Then again, you might get lucky, and the software might run (after a fashion) with just the 1.5 GB of VRAM.

The Age of this computer will Govern what newer version of macOS it will Qualify to install. 

Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install. 

For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence.

Does this computer appear as Listed and qualifying for an upGrade to a newer version of macOS ? 

If Yes, suggest having at least 50 GB of Empty Space on the drive.

It will allow the Full Version ( about 12.xx GB ) to download, expand and then commence to install.

If there is Third Party Security Software installed - remove it.

It will interfere with both the download and installation process.

The below links will help identify which version of macOS  this computer may Qualify to run.

Computer Qualifying for macOS 13 Ventura 

How to upgrade to macOS Ventura - Apple Support (CA)

Computer Qualify for the Monterey upgrade

Make Time Machine Backup  before doing any upGrades