If you want to determine how well High Sierra runs on your present hardware you can follow the procedure in Upgrading macOS without fear. When asked if you want to transfer information from another Mac you can elect to do that at your option, or at some other time using Migration Assistant.
If and when you are satisfied HS runs acceptably well for your needs, you can either upgrade in the usual manner, or restore the contents of that trial installation to your usual startup volume using Disk Utility's Restore function: Restore a disk - Apple Support.
You ought fix operational problems before upgrading. EtreCheck will help with that. Needless to say, if you are using any non-Apple "anti-virus", "cleaning", "cleansing", "washing", "Internet security" junk, anything at all in those broad categories of useless garbage, don't. A lot of things won't work if you do.