One time data conversion in Oracle tables with excel data
If you do not have access to create Directory, then you can use SQL Loader to get data into the database (provided you have Oracle client installed on your system). An outline of the steps is provided below:

a.) Create a table with the same structure as your excel file

b.) Convert your Excel File to .csv format file

c.) Create a Loader Control File. Refer the link SQL Loaer Reference Guide

d.) Go to command line and execute sqlldr command with appropriate format

e.) Verify the bad file and err logs to find if there are any rejections and run them again.

f.) run the update between new table and your existing table.

In case you do not have Oracle Client available, then you can use the data import facility provided in various IDEs like Toad and SQL Developer.