How difficult is it to connect an existing database to a new installation?

Me again!

I’ve had various issues with my installation for a while, but struggled through it for a few years but I’m finding myself thinking that I should try to address them.

I have an existing topic open for something and my jiggles are too numerous to go into here, but I was wondering if starting “afresh” would be a simple enough process?

My site is quite large, I have nearly 4,000 posts on it and many tens of thousands of images. How difficult would it be to “start again” and connect it to the existing content?

Are there people that can do this for me, obviously paid? ??

Thanks for any advice. ??