The following steps will reset the user to: admin and the password to: ubnt@1234
User: admin
Pass: ubnt@1234
This was tested with version 5.5.19

Get MongoDB
https://www.mongodb.org/dl/win32/
OR 32 bits:
https://www.mongodb.org/dl/win32/i386

I used this one:
http://downloads.mongodb.org/win32/mongodb-win32-i386-2.1.2.zip?_ga=2.21740667.1374862506.1502735100...
Unpack it and open a command prompt windows with administrator privileges, switch to the MongoDB’s bin folder

Connect to Mongo
mongo --port 27117
Issue Commands
\\\\ To switch to the ace database
use ace
\\\\ This will show you the current content: (Yours will look similar to this)
db.admin.find()
{ "_id" : ObjectId("5972094a81ce1f0c4d8af05e"), "last_site_name" : "default", "x_shadow" : "$6$448uNfVk$8R01UFv626/QfEdKjk2ynX7oZWVj3XfHdyFf4nJiqaEmgkhoaV/RT1OkybFUZlP6s3/S4RJwnXSHKVVWCsWh20", "name" : "rootadmin", "time_created" : NumberLong(1500645706), "email" : "email@email.com" }
Copy the string and paste it to a text editor like notepad and make it a single line
replace the value of “x_shadow” with this: (this is the hash for: ubnt@1234 )
"$6$9Ter1EZ9$EUfo05Sa3Bj5hHc63SZd6/cn17MVrHqlEPtz/o1Uwxuv18ZySZu.4n04xUhZB12QExZA9MtkNTKWbQ455TkMG1"
And the value of “name” with this:
“admin”
When you’re done your string should look like this:
{ "_id" : ObjectId("5972094a81ce1f0c4d8af05e"), "last_site_name" : "default", "x_shadow" : "$6$9Ter1EZ9$EUfo05Sa3Bj5hHc63SZd6/cn17MVrHqlEPtz/o1Uwxuv18ZySZu.4n04xUhZB12QExZA9MtkNTKWbQ455TkMG1", "name" : "admin", "time_created" : NumberLong(1500645706), "email" : "email@email.com" })

Switch back to Mongo db and issue this command with the string you just created
db.admin.save({ "_id" : ObjectId("5972094a81ce1f0c4d8af05e"), "last_site_name" : "default", "x_shadow" : "$6$9Ter1EZ9$EUfo05Sa3Bj5hHc63SZd6/cn17MVrHqlEPtz/o1Uwxuv18ZySZu.4n04xUhZB12QExZA9MtkNTKWbQ455TkMG1", "name" : "admin", "time_created" : NumberLong(1500645706), "email" : "email@email.com" })


You're done, try to login with
User: admin
Pass: ubnt@1234