GPU Upgrade

I have a Lenovo Ideacenter, running i7-6700 CPU with NVIDIA GTX 960 w/2GB RAM. I am using Davinci Resolve which relies heavily on the RAM on the graphic card and not so much on the system RAM (32 GB). I keep getting a message that my GPU RAM is full and all I can do is upgrade the graphic card. Based on the system can anyone recommend a suitable replacement card with more RAM. I have seen some cards that cost as much as my whole system did a few years ago. I just make videos for my small YouTube channel of my travels. Budget is limited so nothing really powerful, just a good upgrade. Maybe 8 GB RAM but it need to be compatible with the motherboard Lenovo, Skybay, SDK0J40709 WIN 3259593524725. Please provide suitable recommendations. Thanks