Welcome to the world of merging. I understand your hesitation not knowing what to expect. You've identified a good candidate for merger. First note that the typical path for merger is from the newer one INTO the older one. Therefore, after merge 141 would become 77. You can also begin the merge, look at it and still have a chance to back out if you aren't comfortable. But this looks like a good one.
FIrst, go to Alderton-141, scroll to the bottom left and click on "Initiate a merge. Enter Alderton-77 in ID2. (This will set the proper direction of the merge, but if you forget and do it the other direction, it can be fixed later.) Then you will have several choices when you are certain the merge is good you can select "Merge" but it is always safe to do "Compare". There you will see both profiles side-by-side. You can also select the "Comparison Report on WikiTree+" to see potential results.
If the merge still looks good, select "Merge Them" highlighted in Yellow toward the top. Here you will be at the "Propose Merge" stage where you enter a brief explanation for your proposing a merge. Click "Propose Merge". Then the merge will go to the Profile Managers for both profiles to accept or reject the merges. If you are PM, then your approval is already noted. If you are PM for both, you can go ahead with the merger. If, after 30 days there is no response, there is default approval. At that point, you or anyone can do a final review to complete the merger.
I hope this gives you the confidence to proceed.
