Each individual step is not too hard so just do it 1 step at a time.
Step 1 - Check bios version. CPUZ when downloaded and installed is easy way to check this. If you are not on BIOS F62 then update to this version. That bios may not be compatable with the 2600 so do not panic if the pc does not boot once bios is updated. Will be instructions on the Gigabyte website , and in your mobo manual , on how to update your bios.
Step 2 - Turn power off at psu unit and then hold down power button for 30 secs. All LED lights should go off on mobo. Touch a radiator if you are paranoid about static.
Step 3 - Remove gpu. Unscrew , unclip , remove pcie power cables and then remove from case. I would not put the new gpu back in just yet.
Step 4 - Remove cpu cooler. Depends on what one you have. The stock ryzen cooler just unclips iirc so should be easy. If the cooler seems to be stuck then wriggle a bit but do not try to pull it out or you can rip the cpu out of the socket and something may get damaged. If the PC still boots after the bios update then pull the fan header out and boot up the pc for 30secs or so, this will warm up the thermal interface material and make the heatsink easier to remove.
Step 5 - Clean old thermal gunk off then remove cpu from socket. Or remove from socket then clean , no real difference.
Step 6 - Instal new cpu. Make sure you align the triangle to correct corner and gently wriggle till it slips into position. Lots of vids on youtube showing this part so I suggest you look up some people building Ryzen systems so you can see it done.
Step 7 - I assume the new cooler with the new cpu will have thermal compound on it. If not then apply some to the cpu and attach the cooler. If you watched the videos from above step then you will have seen this done as well. Dont forget to plug in the fan into cpu header on mobo.
Step 8 - Put new gpu into slot ,push down till you feel the rention clip attach correctly then screw it in and attach pcie power cables.
Step 9 - Turn psu back on then hit power button and if everything is plugged in correctly your PC should boot. If it doesnt boot then do not panic there is most likely a cable loose.
Step 10 - Boot into BIOS and check memory is running at correct speeds and that everything is being detected correctly.
Step 11 - Boot into windows and enjoy.
Hope that helps. Hundreds of videos on youtube that show people with little experience building pcs so you can watch them and see what to do at each step. I am sure there are little things I missed but the key point is to stay calm and take your tim