Your best bet is to search online for magazine ads and find the original print of this ad. Buy it, can't be no more then $5-15. Then scan the ad in high rez., you can then enlarge it to the size you are looking at with crisp lines.
Don't know if you can still do it but I used to go to the library and look through old magazines. Life mag. is great because of the large format size. That looks to be a early sixties Bug so it should be easy to find in Life.
You can never "fix" a low rez image and make it look good at a larger size.