There are many things you can do, new floor, new kitchen counter top, bathroom upgrade, or put wifi into the building. All update takes money up-front. But if you have half the building vacant, you're losing lots of money every month. It's hard to suggest with only picture of the building exterior. Have you asked your property manager is there anything you can do to get it rented? Experienced property manager should know the area and the market, they could suggest you what to do, and you can decide where to invest your money to get it ready for rent.
If there is no viewing at all, maybe it's time to check the advertising of your property manager and ask them why.
It took me a while to see the benefits of updating the apartments to get it rented. I used to look at the money spent when updating the apartment and think if I can lease the apartment as it is, it would be great. But then I cannot get the tenants we want, and the apartment being vacant for months, at the end we had to update the apartment in order to get rid of the loss in rent.
We have one multi-apartments building, in one year, when old tenants move out, we update most of the apartments, get better rent and good tenants, and the appraisal value of the building was increased by 100k+. When I look back now, I think updating the apartment is good investment of your money in long-term.