These other guys are right, about the 301. You just want to 301 redirect the entire site.
Not knowing exactly what's 'wrong' with your current site, besides slowly decreased rankings... I'd say that if it were me, I'd probably want a fresh start, too. (A new domain, with a clean backlink profile)!
And since I don't know what your site is, I don't know how your content looks. Besides starting fresh with a new, or CLEAN expired domain, I would suggest taking a look at your content and making sure it's not too commercial-sounding.
Actually, if you want, I could take a look at it, in private of course. Maybe a second set of eyes, reading your content, would be good, to get a new perspective. And if you don't feel comfortable sharing with a complete stranger (me) then try to look at your site from a different angle. Pretend to be a customer searching for "musical instruments" and what their perception of your site is. Forget all the hours you've spent building your site. Pretend you're a consumer and want to be impressed with a good looking, informative and not spammy, site, that answers their question and (I assume) has a non-spammy way to buy "musical instruments"
I know that for myself, I am always WAY too close to the issue (my websites) to be objective in any way. Of COURSE I think MY content is perfect, because I wrote it!!!
Here's one way to do a 301 redirect. There are a few ways, depending on what CMS you use and which domain registrar you use.
https://www.domain.com/help/article/how-to-create-a-301-redirect
Good luck!