I am sorry for not responding sooner but have been out of pocket.
Not a problem. We all have things to do that don't involve computers. 
Okay, I did as you advised and I (first I had to download the Minitool Partition Wizard correctly) and I have read over your instructions and checked out tutorial. I am now ready to proceed and it advises to close all programs and disconect power adapter from computer.
Don't worry about closing all programs. At least one (Partition Wizard) will have to remain open.
Are you sure it said to disconnect the power adapter? Last thing you need or want is to lose power during the procedure. Sometimes it might say to turn off power balance (or words to that effect) but that can be ignored. Do not disconnect the power adapter.
When you get to the final step to actually make the changes, you'll probably get a warning that programs were open and the changes can't be made. You should have 3 choices: (1) Cancel the entire operation; (2) Close open programs and retry; or (3) Restart computer and let Partition Wizard make the changes after the computer reboots. Restart computer is the option you want to select. When the computer reboots you'll get a black screen with white letters saying that Partition Wizard will start in 5, 4, 3... seconds and to press any key if you wish to cancel. Just let Partition Wizard do its thing
I did check to see if I recognized anything on the D: partition that would possibly be needed and the only file would be a Dell file that has my computer information on it. Can I save just that file to another location? I have an 8GB Flash Drive and also regular computer disks.
Yes, you could save the Dell file to another location. Or, as suggested earlier, use just 350GB of the D: partition's free space. Partition Wizard will not mess with any of the files on D: and only use actual free space. Personally, I'd leave the files on D: as is (don't worry about saving them to another location) and just shrink that partition down by 350GB. I think that would be the safest thing to do. You'll increase C: by 350GB and have a smaller D: partition with all files intact.
I haven't downloaded a program to detect for duplicate files yet as I didn't know which program to choose, but I can see on my C: that I have Windows.old and Windows files and I have a file that is named MSOCache that is locked. Is that supposed to be that way?
At this point I wouldn't worry about looking for duplicate files, etc. You have ample free space on your hard drive to handle those duplicates ... just not on the right partition.
Once you've taken care of the free space issue on the C: partition you can take care of additional clean up chores.
I just want to say again how much I appreciate your help and before I do this last step I will wait for a response to my questions. Thanks!
Don't thank me yet. Don't want anything to jinx this!